If I understand this correctly, the FCC has allocated the 4.2GHz-4.4GHz band for radar altimeters. The FCC has also allocated the 3.7GHz-3.98GHz band to 5G. It turns out that the radar altimeters, as manufactured, use spectrum outside their allocated band, down to and including part of the 3.7GHz-3.98GHz 5G band.
Am I missing something?
If a rancher buys a plot of land from 34.42°N to 34.44°N to graze his cattle on, but in actual fact grazes his cattle all the way from 34.37°N to 34.47°N. Then a farmer buys a plot of land from 34.37°N to 34.398°N to grow wheat on. Does the rancher still get to herd his cattle down to 34.39°N to feed his cattle? The cattle have to eat, after all, and cutting down the grazing land by 30% could cause some cattle to starve to death. And the rancher has a vested financial interest in ensuring his cattle are well fed, and that wheat is good eating. And the rancher has always been grazing his cattle there, what right does the farmer have to till the soil on the racher's grazing land? And we, the American public, have the right to buy beef. Why should the farmer purchasing 34.37°N to 34.398°N interfere with my ability to buy a steak?
Does any of this make any sense to anyone?
Unless there's additional information I'm unaware of, it seems as if the design and/or manufacture of the radar altimeter is not fit for purpose. Using 3.7GHz to 3.98GHz for 5G doesn't break the radar altimeters; the radar altimeters are already broken and must be fixed or grounded, because the equipment is broken and unsafe.
If 5G equipment is emitting outside of its allocated 3.7-3.98GHz spectrum then the FCC needs to drop a brick on that of course.
There is no way to build a perfect filter. 5G equipment will emit outside of its assigned spectrum and radar altimeters will receive signals from outside their spectrum. The next important variables are the power of the transmitters and the effectiveness of the receiver's filters (and the sensitivity of the receiver). Radar altimeters have been doing their thing for decades because the previous uses of that band had much lower power.
Your analogy is a great demonstration why reasoning-by-analogy fails, by the way.
Sure, but radar altimeter allocation is 200MHz wide and the gap between 5G and the altimeters is 220MHz. The problem isn't that the filters are insufficiently perfect, the problem is that the filters are hot garbage.
If Boeing needs 3.7GHz-5GHz in order to safely operate their aircraft, then Boeing needs to purchase and own the 3.7GHz-5GHz band. If they only want to pay for 4.2GHz-4.4GHz and nothing but 4.2GHz-4.4GHz, but squat on 3.7GHz-3.98GHz they can pound sand.
This isn't a Boeing-specific issue. Boeing doesn't even make the avionics in question. Some of the manufacturers don't even exist anymore. It's not clear who would pay, or how you'd enforce it.
At the time these units were built, the filtering was sufficient to guard against the known adjacent users of the band (low-power satellite signals). Neither the FCC or the FAA set performance standards to suggest otherwise. Nobody expected at the time we'd be blasting high-power omnidirectional signals everywhere at 4 GHz - outside a few specialized uses, it's a terrible band for wide-area communication unless somebody is motivated enough to build tons of towers...which the cell companies suddenly are.
We can agree that the filters are garbage by modern standards, but they were considered adequate at the time the units were built based on the circumstances.
If Airbus has the same problem, then ground Airbus too.
> Boeing doesn't even make the avionics in question. Some of the manufacturers don't even exist anymore. It's not clear who would pay,
Surely when the parts break, they are fixed, and if they are not fixed, then the plane is either grounded or flies in conditions such that the equipment is not required. There is a somebody who repairs, services, or replaces broken parts. These parts are broken. So that somebody fixes it.
> or how you'd enforce it.
You'd enforce fixing this broken part the same way you'd enforce fixing any other broken part. When the FAA finally got around to deciding that MCAS was in fact broken, they grounded the 737 MAX until it was fixed.
Everybody's acting like it's not a big deal that this equipment can't handle a signal that is more than 220MHz away from their nominal operating frequency. Certainly if Hasbro wanted to sell Batman(TM) BatWalkie BatTalkies, but they were rendered inoperable by another signal that far from their operating frequency, the FCC would deny the device its operating license and it would be pulled from the market.
> Nobody expected at the time we'd be blasting high-power omnidirectional signals everywhere at 4 GHz
Infrastructure 5g antennas are directional. The mobile devices themselves are omnidirectional, but those are very low power devices.
> It seems to me then the owners of the offending equipment are responsible for the bill. I don't see how you can come to any other logical conclusion.
Because at the time the equipment was bought, it met every applicable federal standard. This would be unfair to the owners who had no way of knowing about the issue.
Also, in nearly every other case I can think of when spectrum changes, the FCC grandfathers in owners of legacy equipment.
> At least I know why cell service at the airport is awful.
I don't think that's at all related, given that we just started rolling out 5G. Plus the bands in question don't travel through walls very well. :/
> Because at the time the equipment was bought, it met every applicable federal standard. This would be unfair to the owners who had no way of knowing about the issue.
At least in Europe, there is precedent that modern use of frequency assignments make older equipment illegal to operate. 4G and 5G have heavily eaten into the frequencies used on stage for event equipment - microphones, IEM, that sort of thing. Many, many pieces can‘t be legally operated anymore, and it‘ll probably be the same in a few years time with the current-gen devices (although I hope I can swap crystals if needed and keep using my stuff).
Radio bandwidth is a scarce resource. If the radio altimeter is transmitting well outside of its boundaries and it creates problems (for any of the parties requirements), it’s the radio altimeters that need fixing. Even if it is expensive to do so.
No it did not meet every applicable law because it is using part of the spectrum it’s not supposed to be using. The only reason wireless communication in general isn’t pure jamming hell is because we abide by these simple rules.
Nah, it's like healthy Western US forests need regular fires, but people moved into the woods, built flammable homes, and demanded all fires be stopped. Now we want to restart taking care of forests but they whine their house will burn. If avionics don't stick to their band, they are at fault.
"Nobody expected at the time we'd be blasting high-power omnidirectional signals everywhere at 4 GHz - outside a few specialized uses, it's a terrible band..."
As I've point out in my post, why on earth wasn't all this sorted out before 5G was allocated the frequencies.
It seems to me that the the powers behind mobile services have railroaded themselves into these frequencies and that the FCC etc. haven't had the gumption to sort it out beforehand.
If 5G deployments broadcast too close to the frequency assigned to radio altimeters then that's something the FCC should have sorted out, but it appears more like the radio altimeters just have bad filters that let too much outside their assigned frequency through. That makes it a problem of the FAA. The FCC isn't responsible for policing bad receivers.
"That makes it a problem of the FAA. The FCC isn't responsible for policing bad receivers."
What do you mean by 'bad' receivers?
Spectrum management, irrespective of country, sets the parameters of every radiocommunication service by notional equipment standards - here that would be the typical intermodulation figures for radar receivers, inter alia.
The FCC and ITU through WARC/WRC - World Radiocommunication Conferences would have been aware of notional equipment standards for radar altimeters at the time the spectrum was allocated (equipment must comply with the standard or it be deemed out of spec - non compliant).
Note: adjacent services must consider interference to their adjacent services, etc. The standards associated with any service can only be deemed old or 'changed' at WRC conferences specifically to avoid the situation we now have here. The real question is 'who fucked up' - i.e.: did not abide by WRC rules (the international treaty/agreement obligations).
Remember, here international rules are paramount BECAUSE aircraft licensed in other countries that land on US territory also have to meet the same international standards for their radar altimeters as those of the US fleet - it has nothing to do with receivers being 'bad').
> That makes it a problem of the FAA. The FCC isn't responsible for policing bad receivers.
Ah, yes. The best thing you can have is tribal mentality in your government departments. Where instead of cooperating to sort problems out you just say "fuck everyone else" and press onward.
Psst! Boeing isn't the only manufacturer affected.
"Airbus has issued Flight Operations Transmission 999.0002/22 (01/10/2022) which describes the currently understood effects of radar altimeter anomalies. Guidance is provided for A320 family, A330, and A340 aircraft for handing these anomalies.
"Embraer Flight Operations Letter 170-001/22 and Operational Bulletin 170-001/22 (01/02/2022): Describe the possible effects of C-Band 5G interference on its E170, E175, E190, and E195 aircraft.
"The FAA has developed a process by which better performing radar altimeters that are able to reject 5G interference can be approved to operate without regard to the AD and NOTAMs. These Alternate Methods of Compliance (AMOC) approvals will be specific to a combination of aircraft model and radar altimeter model. The method of approval will take into consideration the performance of the aircraft/radar altimeter combination, as well as the location and power of the 5G transmitter in the vicinity of the airport. Therefore, the AMOCs are being issued with a list of airports where they are effective. As of 1/25/2022, FAA has approved AMOCs for several models of radar altimeters, installed on Boeing 717, 737, 747, 757, 767, 777, 787, and MD-10/-11; Airbus A220, A300, A310, A319, A320, A321, A330, A340, A350, and A380, Embraer 120, 170, and 190, all Canadair CRJ aircraft, some DeHavilland Canada DHC-8, and some ATR aircraft. These AMOCs are limited to certain airports and specific models of radar altimeters. Pilots should ensure that they have AMOC documentation for their aircraft and airport (e.g. in a dispatch release) before operating at an airport without regard to the 5G AD/NOTAM."
So some altimeters, manufactured by companies supplying all OEMs way hefore 5g was thing, have trouble with 5G now. There seems to be a solution for this old equipment, civil aviation moves on. For once no need to pick on Boeing here. Or on anyone else.
I never said Boeing should pay for other companies upgrades. Maybe I could have said "the companies that own the airplanes"... but I'm not unaware that other companies are affected... that fact was even in the comment I replied too.
As mentioned, this isn't a Boeing-specific issue. This affects every major aircraft manufacturer, as well as a lot of smaller aircraft with aftermarket avionics. Surely Boeing isn't going to pay for the entire industry.
Also, the FAA has no way of knowing if a particular aircraft operator is using a radio altimeter or not. Even if I have one installed, maybe I chose to switch it off. It's also possible I'm using it for situational awareness only (which is still allowed) and not using it to descend below legal approach minimums.
presumably that's why the two spectrums have a 0.2GHz gap between them, which btw is massive. based on 2020 mid-spectrum prices, this is worth a staggering $66B.
We are talking radar here though. Radar in general is more sensitive to noise. It's not a digitally encoded signal like communications. It's looking at the reflections of radio waves and their strength among other things. This is an analog process the sensor is using. Before digitally encoded broadcasting was the norm the gaps between frequencies tended be wider to limit noise. For communication even with analog encodings like AM, FM ect... The noise floor is quite a bit higher before it becomes unusable for communications compared to radar. Radar needs to look at a wider band of spectrum as things will get shifted more from reflection and such. Further it needs to read the much weaker reflected signals. The signal is weaker because lots of energy will be lost by the time it's reflected. So it's quite possible some higher order harmonics operating on the edge of the 5G spectrum could bleed into the frequency area the radar is using above the expected noise floor.
Keep in mind these sensors were designed and approved long before the FCC allocated this spectrum above this range to 5G. 200 Mhz may be massive for communications, but not that is not entirely true for radar.
The FAA and FCC need to figure out what to do, but the above comment isn't the consideration they need to be worried about.
> Radar in general is more sensitive to noise.... The noise floor is quite a bit higher before it becomes unusable for communications compared to radar
This is not true. A radar has the huge advantage of knowing what signal was sent and only looks for returns that are similar- the FMCW radars in question often mix the return with the originating signal, and outside interference just doesn't cohere and won't affect the result unless the interference is very high power. Radars do not need to look at a wider band of spectrum, reflections do not change the frequency and the Doppler shift a radar altimeter (looking straight down) needs to accommodate is minuscule. A radar that can't handle noise is poorly designed, not that they are inherently susceptible to noise. Radar does require "high" transmit power to easily detect returns, but they can be robust to noise. A radar (including RA) can integrate over a relatively large window if needed and detect with an SNR <1 if it's designed that way.
Whether the old 737 RA was properly designed and can handle the interference, or if they took shortcuts because saving a buck took precedence is a different discussion than the (incorrect) generalities about radar presented in the above comment. Whether the existing RAs can be retrofitted with better filters for cheaper than lobbying the FCC is also unclear, but we know what approach the airlines are attempting right now.
It is more sensitive noise. I did not say it was impossible though to design radar with a higher noise floor in mind. Like the main reason this is problem is not really Boeing's or Airbus's fault. It's only now the FAA went wait a minute when they could have been looking at this years ago since the FCC did announce this quite a bit ago now. The allocation here in the US is closer than to other countries so spurious emissions from 5G equipment and higher order harmonics could possibly be larger issue.
"A radar that can't handle noise is poorly designed..."
I agree with the general tenet of your post but do we know what the status of the radar's RX's front end is like in practice?
From my experience, many of the front ends of older radar receivers are primitive by comparison with today's state of the art in that they have very bad crossmoduation figures (basic diode mixers etc.).
In support of this comment, as a radio astronomer I used to think I understood radar. Then I sat in a presentation by some smart people from MIT, and it turns out that I was really wrong, but the things actual radars do are built on top of things that I know from astronomy.
Radar for an altimeter since by it's very nature it needs to measure distance and not just speed is going to be frequency modulated. Unmodulated/continuous frequency radar can only measure speed. When you start processing the small amount of doppler frequency shift from reflections with a changing frequency things get tricky especially when one has have multi-path return (aka it's reflecting off multiple objects) This will lead two or more reflections with roughly the same frequency, but they have a phase shift. That's the kind of shift I am talking about here. The more noise you have the more difficult it is to separate these reflections when processing these signals.
Edit: I will add the a fair amount of interference by multi path return can be mitigated by making the transmitter and receiver shielded from other directions and designed to be highly directional. This also is generally not to hard to do for an altimeter since the datatum one is measuring after all is just elevation over a small area, compared to something like radar for topography that wants to cover a large area.
Okay, sure, you frequency modulate your output. But the frequencies you get back should be almost identical, right? That doesn't explain why something 200MHz away would interfere.
Yes, they will be very close in frequency. If you have multi-path return you will have two more or more frequencies with different phases. The problem is not so much this alone. All transmitters will have spurious emissions of some level and also your going to have higher order harmonics of the root frequency that will be outside the allocated spectrum. The higher the transmit power of a transmitter the more higher order harmonics you will see above the noise floor. At least for low power transmitters you don't have to worry about more than 2nd order harmonic. Although if you have a powerful enough transmitter like a cell tower 3rd order harmonics can be a problem. Spurious noise is going to depend a lot the design of the transmitter and amplifiers and filters. So how much noise leaks into this bad used for aircraft altimeters is gonna depend alot on the quality of the equipment cellar providers use. Noise can effect radar more easily than normal communication transmissions.
If this were even remotely accurate, the s-band radars that are commonplace for weather radar and maritime radars would be rendered useless by high power telecom/TV BRS and EBS spectrum.
This is a pretty shallow dismissal that doesn't actually provide data to back up the claim. Why would the interference be substantial enough to make them useless? Which weather and maritime radar? There are many at many different bands. What is the meaningful impact of interference on those measurements, and how does it differ from the impact of interference on radio altimeters used in planes during take-off and landing? These are just a few of the reasonable questions that should be answered in such a strong dismissal. Instead, you called it inaccurate without providing any real analysis.
RFI is a problem in these spaces [1]. It's been a problem for many years, and is an increasing one.
I already said s-band (which is 2-4ghz) specifically. BRS/EBS (2.5-2.7ghz) has no meaningful guard band to protect s-band radar, and the radars, at least when used on military vessels, are actually dramatically more sensitive than aviation radar altimeters. And not only has EBS/BRS been operating for decades without any problems, but a) the maritime radar emission/detection patterns are horizontal, just like telecom/television, which should produce more interference than the perpendicular patterns of radar altimeters, and b) EBS has operated for 3 decades using television broadcast power levels...1000s of watts as opposed to the 100s of watts that telecom uses. If interference was actually a problem, the DoD would have shut down those two bands back in the 80s.
Franky speaking, everybody here is talking out of their asses, and just rehashing bullshit that they get told. I'll lowbrow dismissal that all day long because it doesn't deserve and inch more of effort.
I did not say it was impossible to design a radar system to work with a higher noise floor. Also, if you have looked some of the concerns the FCC has in the S-Band range is radar. If you have looked at the frequency allocation rules and such. Quite often around certain frequencies you will see your not to cause interference with radar. However, a lot of radar in the S-Band pulse power tend be quite strong because of atmospheric attenuation, and also noise.
Additionally, lot these weather radars are not trying to achieve same level of accuracy as an altimeter. If the weather formations ones monitoring is off by a little bit, but overall the data is close it's fine. Similar thing with a lot maritime radar, ships are not moving that fast so you also have a lot more time to average out the data. If an altimeter when landing is off by too much can cause a lot problems, especially when you factor in the speeds of an airplane it's you have less time to average out noise or doing other things to filter out spurious noise.
Edit:
Also one other thing about maritime radar there nowhere as much interference once you get outside ports or areas near land.
Also it's not just Boeing here having issues, airbus also along with Boeing has brought this to the attention the FAA. The frequency bands in other countries for 5G tend to be farther away as well from the frequencies used by altimeters so it's not been issue in other countries. It only seems to be handful of air-frames that effected.
Secondly, NOAA have been concerned about 5G, particularly near 24Ghz, again for possibly interfering with radar.
All I was saying is radar is a lot more sensitive to the noise floor and if suddenly that noise floor is higher I am not surprised some equipment will have issues depending on it's use case. Especially, when things were designed long before these new spectrum allocations.
"Especially, when things were designed long before these new spectrum allocations."
See my post about international radio regulations, the 5G service should not have been allocated if it was going to interfere with radar altimeters as that was (and still is) a 'going' service and it takes precedence under international radio treaties.
Thus, an aircraft from a country that's not under US jurisdiction expects to be able to land in the US without its radar altimeter being jammed by some unexpected local service. (It stands to reason that the safety of an aircraft that travels across international borders should not be endangered because of inference to its navigation equipment.)
This is the precise reason why international radio regulations exist! Under the treaty the 'interference' rules apply to ALL radiocommunication services.
If such regulations (standards) are deemed 'old' then they have to be changed at an ITU WRC meeting in Geneva and the item must appear on the meeting's agenda some years before said meeting takes place to give all countries adequate time to respond (as I mentioned elsewhere, I was once involved in that process).
It was not considered massive enough everywhere else, though - even when frequencies up to 4GHz were allocated to 5G, the usage came with special regulations related to use near airports.
The distance between the transmitter and receiver is quite important. Signal strength is inversely proportional to the square of the distance. At some distance you are going to have problems no matter how good the filters are. The problem here is that the receiver is mobile.
Aircraft flying over C band satellite dishes (what used to use the current 5G band) used to cause interference to those dishes. In that case the problem was that the transmitter was mobile. Now the C band satellite people will have to fight interference from 5G transmitters in what remains of their band.
With radar, it's actually worse! Received signal strength is proportional to the fourth power of distance (1/r^2 on the way to the target, then 1/r^2 on the way back to the radar).
That's part of the reason 5G is such an issue, despite the ostensibly-large guard band. You need really good filters on the cellular 5G equipment to make sure it doesn't leak into the radar band.
> With radar, it's actually worse! Received signal strength is proportional to the fourth power of distance (1/r^2 on the way to the target, then 1/r^2 on the way back to the radar).
I think that's specifically true when you're pointing a radar at an aircraft, but is not true for radar altimeters.
When you're pointing a radar at an aircraft, the angular size of the aircraft is 1/r^2, so 1/r^2 of the emitted radiation hits the aircraft. Once emitted from the aircraft, the angular size of radar receiving dish is 1/r^2, so 1/r^2 of that radiation is detected.
With a radar altimeter, you're pointing the radar at the ground. The angular size of the ground is 50% of the sphere, whether you're one foot above the ground or 100,000 feet. (...ok, maybe it's like 49.5% of the sphere...) As long as you're pointing it down-ish, 100% of the emitted radiation hits the ground. There is only one 1/r^2 relationship, on the return leg.
Well, 100% of the emitted radiation hits the ground in terms of total power, but the radar is looking for the _closest_ reflection, which is some relatively small solid angle straight down. It doesn't change your conclusion though, that solid angle is independent of the distance to the ground.
> Well, 100% of the emitted radiation hits the ground in terms of total power, but the radar is looking for the _closest_ reflection, which is some relatively small solid angle straight down.
This fixed angle paints a larger and larger circle as altitude increases. If you double your altitude, you quadruple the size of the surface that's reflecting radar back at you.
A bunch of stuff cancels out and you end up with 1/r^2 at the receiver, which is what we started with.
An alternative explanation is that you treat the ground as a flat mirror, and the radar detects the distance of your mirror image. The distance between you and your mirror image is (2r), so the signal strength you receive from your mirror image is ~1/(2r)^2, still follows 1/r^2 .
I’m not arguing with the idea most of the signal gets to the ground, but, I’m worried that you get specifics quite wrong. Planes don’t want a reflection from 50% of the sphere. They want it from directly below. Other land is further from the plane and obscures the measurement.
But they’re not broadcasting to the whole sphere either, because the radar instrument is not an isotropic radiator. That antenna has gain. It’s louder / more sensitive in a specific direction. Probably by a lot. You can’t make perfect antennas, but you don’t need any signal at all from most of the sphere, so you can gain many decibels.
The angle of the beam you do have is probably fixed, and being fixed would imply that the area swept by the core of the beam is indeed proportional to the square of the altitude. But I don’t think two trips through an n^2 distance is n^4 unless I’m missing some of the physics. Shouldn’t it be (2n)^2 and this still proportional to the square of the altitude not to the hypercube? (And affected by scattering and bad reflectivity from the terrain, which seems likely to be independent of altitude?) This is different for detecting random entities in free space where most of the first n^2 trip really is lost.
So it’s like you say but for different reasons??!?!
The altimeter does not want to know the average distance to the ground over a several square mile region. It wants to know the distance to the ground directly under the aircraft.
Let's not also forget about drift on these filters. Those components will experience drift from age. That drift can also be accelerated from quiet a few factors such as heat ect...
"That's part of the reason 5G is such an issue, despite the ostensibly-large guard band."
As I keep repeating here, if excessive or debilitating interference is being experienced between services under normal operating conditions then there has been a failure of Spectrum Management planning - absolutely no question about it.
OK, we know such interference has happened, so who was responsible for the planning fuck-up?
I've no argument about filters, RFI etc., what most are saying about the engineering issues makes sense.
My argument is that the spectrum planning has failed and that much of the reason can be put down to deregulation in the 1980s when many governments essentially washed their hands of Spectrum Management (succumbed to commercial pressures and overly loosened engineering standards and now we're paying the penalty).
It seems to me (given the international nature of the problem with non-US registered aircraft flying into US airspace, etc.) that we need to go back to the core of the problem and acknowledge these past 'regulations' errors before the problem can be fixed properly.
Perhaps all radar altimeters will have to be changed (respecified with much tighter filters, better intermod figures, etc.) but given the fuck-up who should pay? After all, it's not the FAA's fault nor that of the aircraft industry (see my comments in other posts about the ITU and WRC).
As I see it, this is a political issue, not a technical one.
And many hundreds of emitters. All those towers and phones pumping out 1s and 0s will occasionally line up in a way thay looks like a higher/lower frquency. The aircraft looking down sees across multiple cells. All sorts of strange combinations might occur. Thats what guard bands are for.
Right, so, the issue is NOT the BTS that is being raised, it is the phone on the plane, which are a lot closer to the antenna on the plane, which is on the ass end of the plane which is the low point during take off and landing.
I have run the numbers and there is no way even at phone full power that it can interfere unless it was less than 2m away even then it would have to be free space, etc.
the body losses, airframe, antenna back scatter all taken into account, very very unlikely unless the radar bandpass filters are from the 1960's
The conclusions in the report are more severe than your comments are presenting. I don't think this is a good forum to discuss it further though. There is another comment suggesting a clash of two vastly different safety cultures that really hits the nail on the head, and I think that even the hypothesized/speculative risk to aviation needs addressing, though you are also probably right that the aircraft industry wants cash from the telcos for a retrofit that they should pay for themselves and were willing to drag their feet assuming FAA would trump the FCC in this matter (they will). Frankly if they want digital pulse-compression radar altimeters that are going to operate even with adversarial interference, I built/am-building the most advanced matched filter in the world though it will cost a bit more than a sub-$1K High Pass Filter plugged in line with the antennae which is probably sufficient (though avionics safety requirements will probably find a way to make it $100K anyway)
Thanks for sharing. I’m going to read this report now. Are you in Radar? Potentially looking for a job at a well-funded startup making very high powered phased arrays in c and x bands?
> Your analogy is a great demonstration why reasoning-by-analogy fails
It's a matter of understanding what the analogy is giving you. In many cases, as above, it's merely a foothold, a way of getting started understanding what something is through partial identification with something already known. From that point, the differences between the two can be clarified.
You can think of it in terms of compressing descriptions: let's say you need to describe an SUV to someone; you could start by saying "it's like a truck but [...]," and remove a lot of the redundancy you'd get by starting from scratch.
AFAICT people who think there's something wrong with reasoning-by-analogy are analyzing it with the false assumption that people are just doing "X is like Y" rather than "X is like Y EXCEPT [...]," while also having an understanding on some level of the imprecision/limits of the partial identification.
That people are out there reasoning with analogies thinking they form perfect, limitless mappings between the domains involved seems like an imaginary problem.
There's no perfect filter and no perfect transmitter... correct. But the devices are required to accept reasonable interference and I guarantee that the 5g transmitters don't produce unreasonable interference. This is an issue, like has been said, of poorly manufactured/broken altimeters.
> Your analogy is a great demonstration why reasoning-by-analogy fails, by the way.
I hate reasoning-by-analogy in general but in this case it sounds fine to me. Boeing are grazing their cattle on someone else's land - they don't get squatters rights because no one else was using it at the time when they built their fences. Because it was contractors that built the fences and Boeing didn't perhaps know they were using someone else's land then they should get a little time to move the cattle - or the FAA/FCC can arrange a deal and give the telecom companies some new land - but it's Boeings problem.
Fair, but if we are to expect a certain level of "drift" outside of designated bands, does that mean that the gap between allocated bands should increase?
That is to say, if precision is an issue, what the most effective solution to deal with that lack of precision? From the sounds of it, the technology is unable to comply with the bands allocated, so the regulations around how those bands are distributed should be far more strict, right?
Don't The FCC set maximum levels of noise a device can emit and minimum levels of noise other devices must tolerate. Unless the antennas are way above their limits this shouldn't be an excuse...
In a way, this is a case of disagreement on both accepted levels of noise generated by 5G equipment, and how big the noise is in reality, with FCC having very strong lobby to push through, while FAA having very strict safety requirements (and extra reason to avoid cutting corners after the MCAS fiasco)
But the FAA don't set the noise tolerance limit, the FCC do.
And so far, despite weeks of work, no one has shown anyone is breaking the noise generation limit.
What confuses me here is exactly the FAAs safety requirements: they've said there could be a problem. But they've also not done any research to assess it. And they're not grinding any planes. So they apparently aren't that bothered by safety!?
Note the telco industry have attacked and politicized the research, but they have not offered up their own data to back up their claims. The aviation industry is on much stronger ground here.
And as another commenter put it so eloquently, the aviation industry assumes something is dangerous until proven safe, not that something is safe until proven dangerous.
Noise tolerance limits for SOHO gear or telcos are completely different to requirements on FMCW radar transmitting a signal across all of 200MHz band...
There is ongoing body of work, done internationally, for several years now. They aren't grounding planes because there's no operational need to right now - worst case expect a lot of canceled flights and maybe Southwest going bust as their scheduling flaps too much (also, USA is a bit lucky in having lower need for Category II or worse approaches than some other countries).
And as someone else mentioned in comments, there are already issues cropping up with malfunctioning 5G transmitters despite 400MHz guard bands...
>High power radio bandpass filters allow for guard bands on the scale of a single mhz.
Not at 4GHz. This stuff works in terms of percentages of the frequency in use. The higher the frequency the larger the guard bands required for any sort of practical filtering.
> Radar altimeters used in civil and commercial aviation operate using either unmodulated
pulse radar or frequency-modulated continuous wave (FMCW) radar technology, with
FMCW being far more common among models developed in the last few decades. In either
case, the above ground level (AGL) altitude of the aircraft is measured in the radar altimeter
by transmitting radio frequency (RF) energy down to the ground and receiving a portion
of this energy back through reflection off of the terrain or other obstacles, and determining
the round-trip propagation time of the RF energy. The radiated power levels are low,
typically on the order of one watt, and thus highly sensitive receivers are required for radar
altimeters to function properly. As such, radar altimeters are highly susceptible to RF
interference entering the receiver, which can negatively impact their performance.
The planes use the band to bounce signals off of the ground and that needs to be super sensitive. That's why they probably can't afford to properly filter within the 200 MHz guard band.
Your analogy is slightly oversimplified because it assumes a fully functional fence (probably two, with a road between them) between the wheat fields and the cattle. The cows might gaze longingly across the road at the wheat fields and the wheat farmer might smell some manure while harvesting, but the fence is fully functional. In real life, a 2200 lbs steer might not think much of a mere barbed wire fence or high-voltage tickle separating it from the wheat field...but that's stretching the analogy a bit too far into the weeds.
A better analogy needs to understand that the filter on both sides of the equipment is imperfect.
Replace the altimeter with, say, Mount Rushmore National Monument, and replace the wheat farmer with, say, a putrid landfill, sewage processing operation, or CAFO chicken farm. Neither the monument nor the viewing areas extend beyond the surveyed boundaries of the monument. But part of the appeal is that it's a pleasant, quiet, natural place in the middle of a national forest: abutting it with something smelly, noisy, or ugly might be legal but would harm it even though it doesn't extend past the property markers.
Personally, I do think they need to upgrade and phase out the altimeters to be more tolerant against interference. But they're not necessarily broken, just too slow to adapt past the scope and capabilities of the tech available in 1967.
> If a rancher buys a plot of land from 34.42°N to 34.44°N to graze his cattle on, but in actual fact grazes his cattle all the way from 34.37°N to 34.47°N. Then a farmer buys a plot of land from 34.37°N to 34.398°N to grow wheat on. Does the rancher still get to herd his cattle down to 34.39°N to feed his cattle?
> in the English common law tradition, courts have long ruled that when someone occupies a piece of property without permission and the property's owner does not exercise their right to recover their property for a significant period of time, not only is the original owner prevented from exercising their right to exclude, but an entirely new title to the property "springs up" in the adverse possessor. In effect, the adverse possessor becomes the property's new owner.[2][b] Over time, legislatures have created statutes of limitations that specify the length of time that owners have to recover possession of their property from adverse possessors. In the United States, for example, these time limits vary widely between individual states, ranging from as low as three years to as long as 40 years.
Also, in some states like California you have to pay taxes on the land for a certain period of time before you can claim ownership.
But yes, in your specific case it is possible to raise cattle on someone else's land for long enough to be able to legally claim that land as your own.
I think what you're missing is that assigning blame isn't especially helpful. those altimeters are already in the airplanes. those planes are serving an important purpose, and grounding them until they can be fitted with altimeters that only operate in their allowed spectrum would be more harmful than disallowing 5G equipment from operating in that spectrum.
a rancher allowing his cattle to graze outside of his allowed land doesn't result in a fiery crash that kills hundreds of people.
you're right, the planes are in the wrong and they should be fixed. but that's kind of not the point.
Postpone the 5G allocation, make the altimeter manufacturers/users pay market price for the spectrum to those that would have gotten it allocated until they can return the spectrum, and also pay a fine to the government for using spectrum not allocated to them (in the past, current and future breach covered with the rent mentioned before).
And give some timeframe by which spectrum must be returned.
The radar altimeters aren't "using" (in the FCC sense) any of the 5G spectrum. This is an issue on the receive side. The FCC primarily regulates transmission, and the transmitters themselves are compliant. The FAA's TSO-C87 doesn't have any requirements for rx filtering either. So there's no legal grounds to fine anyone.
That is exactly what's been happening. The FCC has continued with the 5G rollout, and the FAA published a NOTAM prohibiting use of radio altimeters on approach until each model can be proven safe.
However, folks are now unhappy because that means no Cat II/III approaches, which means airliners can't land in fog or bad weather... which means significantly more airline delays while all this gets sorted out and equipment gets recertified or upgraded. Consequences.
(Also, fwiw, the avionics aren't built by Boeing, and this is not a Boeing-specific issue. It impacts other aircraft from all manufacturers.)
It affects Airbus A220, Airbus A330, Boeing 737 and Boeing 787 most notibly.
In that it's mostly a US-issue (Europe has much better protection in this area, i.e. that 5G antenna must be directed downwards, the 787 is the biggest issue, as those are doing international flights with other carriers to US airports.
"...and let the clowns at Boeing and the FAA handle the fallout."
It's NOT their fault!, See my other posts about the ITU, WRC and international radio treaties.
This issue has more to do with Spectrum Management planning failures and goes back as far as the 1980s when governments washed their hands of the matter and 'deregulated' spectrum matters because of commercial pressures. Moreover, they loosened the engineering (interference) specs now we're paying dearly for the fuck-ups.
You work with providers to measure impact and to reduce interference around airports. You issue NOTAMs (Notice To Air Missions) to all pilots know where this 5G interference is known to be a problem, and you wrap it all up with AD (Airworthiness Directive) for the 737 itself which specifies that those NOTAMs apply directly to the equipment on this make and type of aircraft.
This already happened. 5G roll out around airports has been postponed multiple times. The airlines don't want to fix the problem because it will cost them money. It's time to tell them tough shit.
I'm curious as to why you think the planes should be fixed, but "that's kind of not the point"? It seems to me that it's pretty far out of the frequency boundaries.
Yes. In your example, the government may decide to temporarily allow the rancher to keep grazing his cattle until the rancher can reduce the size of his herd, because they don't want to force him to destroy good cattle, while requiring the rancher to pay the farmer for the use of his land and lost profit from the wheat he cannot grow.
The alternative would be to force the rancher to cull half of his herd, which would not only be wasteful, but also cause a national beef shortage, while the world so far survived without the extra wheat. So the government does the pragmatic thing, even though it shouldn't, according to the permits it issued. Probably wouldn't happen with beef vs. wheat, but I could see it happen with beef vs. corn-for-ethanol, because food safety trumps ethanol production.
The FCC might decide that existing aviation needs beat not-yet-established mobile phone needs. Whether the spectrum owners would actually be compensated fairly, or whether the government would the "you're getting screwed over because I like the rancher more, I've got the bigger guns, what'cha gonna do about it?", - that I don't know.
But from the article, it sounds very much like the FCC isn't doing much except having told the farmer to wait a few months before plowing the greenest grazing land to keep the peace, and the FAA is telling the rancher "your not-your-own grazing land is gone so your cows might starve, deal with it".
The difference is that cows don’t fall from the sky and kill hundreds of humans in the process.
“Fix the thing” is the correct answer, but managing risk in the meantime in this regulatory environment is a shade of grey. Doing nothing puts people at risk. Grounding aircraft cripples a critical industry. Delaying 5G costs two network operators a lot of cash.
It is my limited understanding that no EM signal drops off as vertical wall at the exact edge of spectrum, and radar altimeters behave within actual defined requirements and regulations. The land analogy is useful exactly to the point where it is deceptive / misleading (no ill intent is assumed here! We are all just trying to figure it out :). Land behaves like land (nice and discrete and binary with a thick clear line) and waves, well, like waves :-)
> It turns out that the radar altimeters, as manufactured, use spectrum outside their allocated band, down to and including part of the 3.7GHz-3.98GHz 5G band.
Did the FAA say this is what's happening for sure? If so that answers a lot of questions I've had because like you said they are on different parts of the spectrum so it should not be an issue unless something is operating out of spec.
So, here's what's actually happening in a nutshell...
The FCC allocated a specific band for radar altimeters to transmit in. The FCC only specified rules on transmission, and the radar altimeters are 100% compliant with the FCC rules and only transmit within their assigned band.
The FAA published TSO-87C, which is the technical spec for the radar altimeters. But this also just covers transmission and performance. There's nothing in this spec about rejecting external interference. The radar altimeters are compliant with this spec as well.
The problem is on the unregulated receive side. All radio signals have some amount of bleed-over into adjacent bands due to harmonic interference. Historically, the adjacent frequencies were used for low-power satellite communication, and the manufacturers added enough filtering to protect against the harmonic interference from these low-power stations. They did not anticipate a high-power (5G) signal in those adjacent bands, and nothing in the FAA/FCC specifications protected against it either.
So it's not that the radio altimeters are "using" the adjacent bands, but the receive filtering is (in some cases) insufficient to account for the new (louder) users of the adjacent bands.
What I'm confused about is, why are the FCC and FAA suddenly running into this problem now? Hasn't 5G been coming for a long time? What did they expect would happen instead?
The decision to sell frequencies as close as 220 MHz away from lower end of radar altimeter band came only in 2019, and aviation world already been working on possible interference at the time - which led to much higher guard bands everywhere else and/or extra requirements on use of 3.8-4.0GHz allocations, especially in terms of usage near airports.
The issue is that the FCC sale of frequency spectrum up to 3.98GHz doesn't have such limitations, so essentially in 2019 aviation got an unique problem of extra heavy interference in USA
"5G" doesn't refer to one specific set of bands. Radar has been operating this way for decades, and only last year did the FAA decide to allocate the nearby spectrum to high power transmitters.
Yeah so we circle back to my original question: What did they expect would happen instead? Why didn't they do anything? The problem wasn't going to just disappear randomly right?
Two different government agencies with different incentives.
The FCC really wants to proceed with the 5G rollout. The FAA really wants to make sure aircraft don't crash. They do not agree with each other on this, so they each proceeded in the only way they administratively could...
The FCC continued with the 5G rollout, the the FAA recently banned use of approaches requiring a radio altimeter until each individual model can get recertified or upgraded - and the public will just have to tolerate additional travel delays for the next couple years as a result.
I can't say if it's right or wrong, but in relation to your specific example, there are "adverse possession" laws that grant legal rights to the occupier of land in the US.[1]
It's the receiver, so it's more like, you're asserting your right to leave your door wide open on a street that is suddenly much more busy.
De facto possession of spectrum was heavily litigated in the early days of radio. There basically is none (not legal advice!), essentially no one has a claim on spectrum in the USA that is not assigned or regulated by the FCC. You have to sign away any claim to spectrum from before the establishment of the FCC to get a ham license or similar radiotelephone licenses. Nobody is around anymore that was operating then anyway. The language is blandly bureaucratic but in context that is what it means: "The Applicant/Licensee waives any claim to the use of any particular frequency or of the electromagnetic spectrum as against the regulatory power of the United States because of the previous use of the same, whether by license or otherwise, and requests an authorization in accordance with this application."
There is probably some similar language in the applications for other licensed bands.
Regardless of whether this makes sense, the hypothetical scenario you describe is called "adverse possession."[0]
Now, it may be that spectrum doesn't count as property (especially since the FCC's existence derives from the fiction that "the public owns the airwaves"). This situation makes something of a mockery of that FCC narrative, since no one believes these airplane radars will all be replaced at the drop of a hat, but nevertheless it would probably hold up in court as a matter of law.
I have no idea how the government could try to remedy this situation. Seems like admitting adverse possession with some sort of compensation and/or trade in spectrum might make sense.
It’s more like, you can fence off your cattle but you can’t fence off the birds and the bees.
So even if the cattle stay within their limits, the grass relies on bees coming in from neighbouring farmland to stay healthy.
If you pave the area outside a cattle ranch the grass inside will die on the borders.
So you have to zone the land outside the fences to make sure it some other ranch or else left wild.
The same with spectrum. Adjacent frequency bands have to allocated to uses which do not produce a lot of interference that travels very far or is used very much.
These bands are not like drawing two parallel lines that don't touch, then blaming the other person for coloring outside the lines. An exclusion band is allowed ±10% around the band within which the HIRF levels are very low. For radar altimeters this spans 3.78–4.84 GHz.
This is about money, the airlines want money from the telcos.
The telcos paid off the Incumbent Earth Station operators to vacate the spectrum, now the airlines have their hand out because they are cash strapped after a pandemic lock down.
I have read this carefully, and run calcs myself, the issue they are raising is the phones on the plane. But even at full power, very unlikely, but read my other post on this for more details.
The real issue is that they want the telcos to pay them to swap out their radar but are asking for a large amount beyond what would be needed to do that.
"Unless there's additional information I'm unaware of, it seems as if the design and/or manufacture of the radar altimeter is not fit for purpose."
Whether radar altimeters in their present form are fit for purpose or not I cannot answer as I have insufficient information to do so. However, I must point out that:
1. ALL radiocommunications have limitations in that they can suffer interference from other services even when those other services are operating correctly and according to license (i.e.: being in their correct allocated frequency bands and operating at their correct power levels, etc.).
2. The role of Spectrum Management falls to the FCC. It operates under the auspices of the ITU (International Telecommunications Union) to manage the spectrum through its international treaties and its job is to ensure that interference between services is kept to a minimum. In essence, the aim is to maximize spectrum usage whilst keeping interference to trivial levels (it should be noted however there's no such thing as 'no interference').
(International treaties are necessary as electromagnetic radiation doesn't honor a country's borders.)
3. The way this is achieved is complex but in essence transmitter frequencies, power levels and transmitter locations are optimized to provide optimal protection ratios to each service so they can operate efficiently.
4. If services are mobile, as with radar altimeters, one of the parameters used in optimizing protection from interference is lost. Signals from radar altimeters can interfere with other services and vice versa as they can get too close to one another (interference increases significantly when powerful transmitters are close to sensitive receivers).
5. How tightly services can be packed together depends on many factors but two principal matters stand out: the laws of physics and the state of the art of electronics design.
The major culprit in causing interference is a well known form of distortion whereby several radio signals can interfere with one another to produce multiple other freqenies that are harmonically related to the original frequencies. This interfere is called intermodulation distortion and it's one of the perennial scourges of radiocommunications: https://en.m.wikipedia.org/wiki/Intermodulation.
For example, a transmitter on f1 (service 1) and another say on f2 (servive 2) can produce other unwanted frequencies, f3, f4, f5, etc. that can interfere severely with unrelated services. Under some circumstances interference to the unrelated service can be so severe that it can be rendered useless (as mentioned, this can be very problematic when services are mobile as it's very difficult to take every contingency or location into account).
6. These matters become much more critical when the stakes are high - with emergency services, radar altimeters, etc. where lives can be at stake if things go wrong.
7. Critical communications services have always demanded very high protection ratios and have traditionally been given them by Spectrum Management agencies - the FCC, et al. The current argument is that the ubiquity of 5G threatens the high protection ratio previously afforded radar altimeters.
8. If I were in the aircraft industry and I was responsible for the reliability of safety devices such as radio altimeters then I'd want to be absolutely certain that any new radiocommunication service is not going to interfere with any of my critical services. Moreover, I would be overly concerned with the potential for mobile phone services to interfere with these safety services specifically because phone services are a never-ending moving target when it comes to location, density of phone traffic, etc., all of which have potential to cause interference.
9. Whether 5G has real potential to interfere with radar altimeters or any other aeronautical communications service can only be determined by proper independent engineering studies.
The fact that we have this dispute at this late juncture shows that something has seriously gone wrong in the planning phase.
(From my observations, it seems the mobile phone industry has had too much political power, especially so when it comes to buying spectrum - and it has lots of money to demand what it wants (and to date it's gotten the spectrum it wants). Whilst government eyes the millions to be made from the sale of spectrum, the trouble is that it's also the regulator of the spectrum hence it has a conflict of interest.
Fundamentally, spectrum auctions run by governments have the potential to compromise good spectrum management. Whether it's happened in this instance I cannot say for certain.
The only other point I'd stress is that the electromagnetic spectrum is a scarce nonrenewable environmental resource and should be respected and treated as such (like any other environmental issue).
It's probably not good to nitpick but with the land analogy you have zoning (the lack of zoning that led to the West Texas disaster comes to mind) and animals (bees etc) tend to cross land boundaries so it's not quite that clear cut.
It all does sound a bit silly though. I will say I wish the FCC was as happy handing spectrum/power to unlicensed users as it is to what are nearly exclusively Qualcomm customers.
I don’t know much about aviation or electrical engineering, and I’m wondering if anyone could help me understand something.
It seems like the telecom and aviation industries (along with the FCC and FAA) disagree on a question of fact: does 5G equipment interfere with radio altimeters?
There’s a way that the FAA could convince me, and probably all the politicians. Shoot a video with a radio altimeter and some 5G equipment where the radio altimeter malfunctions. Put it on YouTube. Do a press release.
This seems like an obvious step if the underlying issue exists. Any reason they haven’t done this?
The question isn't really whether the radalt fails in any particular test (spoiler: it probably won't). It's whether there's an edge case where the safety case for the aircraft depends on correct operation of the radalt AND there's a failure. I haven't seen the fault tree for the 737, of course, so I don't know what reliability is required from the radalt to be safe; but with the radalts I've worked with it's not unreasonable to have an undetected failure rate requirement of 10^-8/hour or better. (Detected failure rates can be much higher.) Testing enough to show that you're not violating that is /hard/.
Speaking a bit from my own experience, I suspect the guard bands on most radalts out there are wide enough that 5G interference isn't a practical issue. I've seen radalts with 30 MHz guard bands around the 4.1 GHz / 4.3 GHz limit frequencies of interest... and that's friggin' huge. (I'm also sure there are radalts with much smaller guard bands that use more of the available bandwidth for better performance.) But this is hard to analyze fully. Taking the example of the unit I'm thinking of, the center frequency is from a non-temperature-compensated oscillator -- so your worst case is an extreme temperature going to assymetric guard bands, a unit with a weak bandpass to begin with, and a 5G system pouring a lot of energy at (or even, in violation of spec, a bit beyond) the edge frequency. Probably fine. 10^8 fine?
> The question isn't really whether the radalt fails in any particular test (spoiler: it probably won't)
Annecdata, but... I know two commercial pilots who have both recently run into interference with their radar altimeters during landing/takeoff. It certainly doesn't affect all aircraft (depends on the particular avionics installed), but from what I've heard it is a real issue.
It's not so black and white. From what I've read, radio altimeters operate in the 4.2-4.4 GHz range, and the 5G spectrum in question is 3.7-3.98 GHz. RF systems generally work by choosing a center frequency (say 4.3 GHz for altimeters), and trying to filter off anything outside the band of interest (4.2-4.4 GHz). The junk that remains is noise as far as the system is concerned, and has to be budgeted for very carefully.
The problem is that radio altimeters are pretty old, and their filtering technology is not great. So even though they are filtering the 3.7-3.98 GHz 5G band, it's not as effective as a modern RF system/filter would be. Previously, this wasn't the issue because nothing was broadcasting in that band at particularly high power.
That's the second component of the problem: power. The radio altimeter system is capable of handling some amount of noise power caused by unwanted broadcasts, among other things. Previously, satellites were using this band, and they were so far away that between the distance-based attenuation of the signal and the limited filtering, radio altimeters could operate unaffected.
5G is a different story, though. The towers are much closer to the runway, so the leakage power is much higher. Whether this actually causes a problem for the altimeters is then dependent on a number of factors, including the distance to the 5G tower, the transmit power level, the direction of the 5G antennas, etc.
Could it cause a problem? Sure. I bet if you pointed a directional 5G antenna straight at a particularly crappy radio altimeter, you could materially affect its operation. But there are many mitigation strategies that could be used, like requiring lower transmit power, further antenna distances, appropriate directional transmissions, etc. These strategies have been used successfully in other countries.
The real concern should be the total lack of collaboration between the FAA and FCC. It's turning into a jurisdictional pissing contest.
AFAIK it’s not so much a lack of collaboration. It’s more nuanced than that.
The lower frequencies used by Europe for 5G are already allocated for amateur and other uses here in the US. I believe Europe has been more willing to take away amateur bands.
However here in the US, the FCC was trying to maintain those existing allocations and thus they chose to reuse 3.7-3.98 GHz instead, which is currently allocated for fixed satellite and other links.
Therefore what FCC did is potentially better for everyone, if we can find out that radio altimeters—which should be filtering out frequencies that never belonged to them—are still able to work correctly.
The issue is that, as you may know, if you engineer for something but don’t actually regularly test for it, you never actually engineered for that case. Up until this point, this case was never tested in production… because it has never existed in production.
At the end of the day, we are between a rock and a hard place.
> The problem is that radio altimeters are pretty old, and their filtering technology is not great. So even though they are filtering the 3.7-3.98 GHz 5G band, it's not as effective as a modern RF system/filter would be.
and actually not only are they old but they are defective - they were designed to function with guard bands half the size that the FCC ended up giving them, and they still are running into interference. They are basically picking up way way way more than they were originally specced to, and that's suddenly a problem because somebody moved in next door.
also to my understanding it's specifically a problem with Boeing and other aircraft are much less affected. So we are also running into the "boeing has become a quasi-state enterprise that is too-big-to-fail and will be protected under all circumstances even when they do something obviously dangerous", like the MCAS system on the 737 MAX.
honestly I kind of feel like the real situation here is that Boeing needs to issue an airworthiness directive and have those altimeters replaced. If a wing broke at half the loading spec, we wouldn't hesitate to say that's faulty and should be replaced. But with guard bands twice as wide as initially specced these altimeters are still having problems? Get them out of the air until Boeing fixes them.
> The real concern should be the total lack of collaboration between the FAA and FCC. It's turning into a jurisdictional pissing contest.
they were collaborating a long time ago - but again, there is only so much you can do when it suddenly turns out that a 2x margin of safety from the design spec (which itself incorporated a margin of safety) is not nearly enough.
the spectrum was sold a long time ago. the airworthiness certificates were issued decades ago. At this point there is no solution possible that doesn't make somebody unhappy.
I lean towards the party that needs to be made unhappy being Boeing here - but that will make airlines very unhappy as well. Saying "no you can't use that spectrum" is an unconstitutional taking at this point, you auctioned it off for cash monies and that absolutely puts a legally enforceable price tag as a minimum bound - in practice the value is higher since business plans have been built on it. But there is no constitutional right to fly a defective aircraft, if the FAA grounds your plane because it's unsafe that's not a taking.
But that will have a massive impact on boeing, airlines, and the economy as a whole.
Total noob question, why isn't Boeing building/buying new radio altimeters that can filter better? Is it a money thing, a technology thing, maybe both?
It's not just Boeing. Boeing orders certified radar altimeter devices for their configurations, and then certifies the whole assembly of it on a plane. The whole technology of radar altimeters makes it particularly hard to filter out 5G signals at 3.98GHz.
As part of trying to keep flying safe, both attempts to limit sources of interference (i.e. 5G transmitters) and checks on existing hardware (and thus whether it needs to be replaced) are done in parallel. Outside of USA, everyone agreed on various mitigations to limit impact to radar altimeters especially as full impact of C-band 5G is still work in progress.
> "Move fast and break things" doesn't work well with aircraft.
Sure, but that didn’t seem to stop faulty lithium batteries on the 787 or MCAS on the 737-MAX. If only Boeing would learn the lesson, maybe we wouldn’t have these messes.
As has been pointed out several times already, this is not a Boeing problem. It affects practically every major aircraft manufacturer.
If anything, Boeing has been very proactive about identifying the affected equipment well before any accidents happen. This is precisely what they should be doing.
> As has been pointed out several times already, this is not a Boeing problem. It affects practically every major aircraft manufacturer.
1) I never stated the radar issue was only Boeing’s “problem” previously, I stated it’s yet another example of a mess they are in which ultimately boils back to a “move fast and break things” attitude being a major cause (just in this case, it was more the FCC to blame for that attitude)
2) It ultimately is their problem to solve for the airframes they sold however, whether it was their fault or not.
> If anything, Boeing has been very proactive about identifying the affected equipment well before any accidents happen. This is precisely what they should be doing.
Link to the ADs from Boeing saying which models are susceptible? I hadn’t seen that
You're using the wrong burden of proof here. You're assuming it's safe until proven dangerous, while the FAA is (properly) treating it as dangerous until proven safe.
Take the recent 737 MAX debacle as an example. Its MCAS hadn't been proven to be dangerous when it went into production, but it turned out that it was. Result: two airplanes fell out of the sky and 346 people died. It's the FAA's job to prevent this sort of thing from happening, and in this case (unlike the 737 case) they're doing that job.
Thank you! This is the most important and most correct comment on this forum today.
Truly, it's amazing how many aerospace engineers hang out on HackerNews!\s So many assertions about what is right, what is wrong, and who is to blame. 99% of these assertions reflect a poor understanding of how commercial aviation fundamentally and functionally works.
Not only is your comment 100% correct, it also strikes at the heart of the problem. Diplomatically, the issue that exists today is a clash of the very different safety cultures that exist between aviation and telco (and by extension the FAA and the FCC.) Aviation will win, btw. The question, however, is at whose expense.
Btw, the root of all this can be traced back work the aviation industry had undertaken to create a standard for wireless safety critical avionics (a system and standard called WAIC.) It was about four years ago that the aviation industry tried to secure additional spectrum, was denied, and thus started researching how to use the existing 4.2-4.4ghz spectrum already dedicated to aviation. It was through this research that the industry discovered the inherent problems with radio altimeters and nearby spectrum interference.
The aviation industry petitioned the FCC during the notice of comment period for the C-band spectrum sale, sharing the research and the data which shows 5G interference could be a problem given how it was planned to be deployed in the US. T-Mobile did their own preliminary study in support of the aviation industry's findings, but the rest of the telco industry attacked the research done without providing their own alternative data. The FCC, under Ajit Pai, and with support of the telco's lobbying arm CTIA, then effectively politicized any additional technical assessment or study, leading to today's brouhaha. If you want to blame anyone, blame the FCC and their former chair, who btw, is already a favorite internet punching bag.
(Note that T-Mobile is the only carrier that did not purchase the spectrum, although it's not known whether this was due to T-Mobile's own supporting research.)
Agreed, very surprised at the cavalier attitude of many of these comments. I'd rather my phone be slower than my plane think it's 300ft higher than it actually is. Aviation isn't the area to be making assumptions that it "should be fine."
My guess is that RF interference is not binary. So the question is not "Does 5G equipment interfere with radio altimeters?" but rather "Could 5G equipment ever interfere with radio altimeters, under any set of feasible conditions?"
Which is a harder question to answer, but how seriously we should (and usually do) take air safety.
The way you test this stuff is get a rad-alt and inject known amounts of RF and see how much is needed to give false readings. Then you go and measure how much RF you'll see in the environment and see if it exceeds those levels.
Here's a choice quote from the summary: "In the worst case, the safe interference limit for the fundamental emissions is exceeded by over 47 dB, and the safe interference limit for the spurious emissions is exceeded by over 27 dB."
The question isn't can you reproduce it in an artificial setup, the question is can you do it in the real world? I can think of a lot of ways to cheat in the lab (turn the power to 11...) that create situations that in the real world wouldn't happen and so I wouldn't worry about it. However that doesn't change the fact that if you can recreate it in the real world I'm really worried.
I am 40+ year experience in this area, I have run the calcs, the thing they are worried about is the phones on the plane, the phone would have to be less than 2 meters from the radar antenna and at full power to come even remotely close to the interference numbers they are talking about to give a false reading, and that would be without a lot of body loss.
The airlines want the telcos to pay them to swap out their old radar units, it is about money of course.
There’s already been incidents of 5G interfering with ILS on airliners. Which is what planes use to land in bad weather. When bad weather hits a destination airport, you’ll more likely be rerouted to a different airport due to the risks of using ILS now.
Wow, this along with potential interference problems in weather radar [0], it's obvious the FCC bungled allocating the 5G spectrum. What a shame that they gave into industry pressure over other practical considerations.
However, it doesn't surprise me that the FAA, which allowed the Boeing 737Max fiasco, is back here coming to Boeing's defense. What happens when 2 captured regulators collide?
Edit: added spacing and changed "radio" to "radar" for clarity
It's not obvious at all. Boeing shouldn't be using these frequencies and this has been 10 years in the making. Boeing should fix their equipment to operate within its assigned range (+ the huge guard bands they gave them for no real reason).
This is like your neighbor driving onto your lawn, and then demanding you move out of your house. They should drive right back onto their lawn.
I downvoted this comment for the completely wrong analogy and misunderstanding of how radio works. So wrong, in fact, that it is hard to believe it was made in good faith. Still, I am going to treat it as if it were.
The problem is on the radar altimeter's Rx side, not on the Tx side.
The radalt has Rx filters to reject noise on nearby frequencies. Cell towers have Tx filters to avoid broadcasting on nearby frequencies. But no real filter has 100% rejection outside the passband. That means that a 5G cell tower will broadcast some amount of energy within the spectrum defined for radalts. Also, radalts are not able to perfectly reject all energy that is outside, but arbitrarily close to their defined spectrum.
A second factor is that power received by a radar falls as the fourth power of distance between a radar and the target (in this case, the ground). Tx power goes as 1/r^2. The target, having received that 1/r^2 power, then re-radiates it back to the radar, where it again falls as 1/r^2. That means radars have to be designed to detect very small amounts of power. Because physics.
So the combination these factors leads to a situation where the high broadcast power of a cell tower inevitably leaks some energy into spectrum near that which radalts operate in, not all of which is effectively attenuated by the radalt's Rx filter. The small amount of energy that leaks past both filters can cause interference due to the sensitivity requirements of radalts.
At a fundamental level, it was really stupid for the FCC to allocate high power transmitters in a band right next to radars. This is starting to be a pattern: See the attempted Light-Squared allocation next to GPS (for which the received signal strength on earth's surface is lower than the thermal noise floor).
Based on the number of comments confidently proclaiming that radalts are somehow using spectrum they aren't supposed to, I'm starting to think that HN is being heavily astroturfed on this subject.
> This is like your neighbor driving onto your lawn, and then demanding you move out of your house. They should drive right back onto their lawn.
No, this is like your neighbor planting some very delicate flower near the property line and then asking you not to spray Roundup all over your property because some of it drifts onto his flowers.
What about older planes? I'm not sure if boeing should be responsible for retrofitting all of their older planes just because of change that happened years later.
Boeing's altimeters should have always operated within the frequency bands allocated to them and been resistant to interference from other bands. These altimeters are operating outside the specification they should have met when deployed. This is an utter failure on the part of aircraft manufacturers, airlines and the FAA. They are all screaming loudly to try to shift the public perception to this being an issue created by the FCC and telecom companies.
>Boeing's altimeters should have always operated within the frequency bands allocated to them and been resistant to interference from other bands. These altimeters are operating outside the specification they should have met when deployed.
This is not an extraordinary claim, it’s how all basic radio spectrum allocation works.
How else are you supposed to make sure that equipment made today won’t interfere with equipment made tomorrow if people don’t stick within their frequency allocations?
The claim above is basically the equivalent of “car should have always operated on the roads that are allocated for them, and should never have been driving through empty fields”. If you’re driving your car through a field you don’t own, you don’t get to complain when someone builds a house there.
All radio equipment is meant to be specified to operate only within its allocated spectrum, and to handle RF noise and interference from anything outside it’s spectrum.
How a radalt works is irrelevant, the allocation determines the operating parameters. If your equipment can’t operate within those parameters then it’s faulty, simple as that.
Nobody would try to defend a building whose foundation crept over outside of the plot of land belonging to it. If you’re house can’t standup without putting parts of itself into your neighbours garden, then your house is faulty, not you’re neighbours home when they decide to repurpose their garden.
What's extraordinary about the claim? The guard band between 5G and radio altimeters is ~200MHz, which is massive. If your filtering can't handle signals over 200MHz away from what you're looking at, then it's garbage filtering.
200 Mhz may be massive for communications (especially digital encoded signals), not necessarily for radar when you sensor is receiving weak reflected signals that very likely can have a frequency shift on reflection. So radar receivers need to receive on a wider frequency band than a receiver for communications.
Depending on the strength of 5G transmitters the higher order harmonics could be above the noise floor.
How is it extraordinary? Equipment is typically required by law to operate only within its specified frequency bands. 5G spectrum was never allocated to aircraft radar altimeters.
I agree that quoted suggestion lacks nuance in the history that brought us to this state, but from a technical perspective it does not seem extraordinary. More that it simply advocates a very expensive and uncooperative way to solve a problem of the commons.
Equipment is required to emit only within its allocated frequency bands. No-one is suggesting that the radar altimeters are emitting outside of their allocation; but there's no law that says that devices have to be immune to interference from other transmissions outside their allocated bands.
There’s definitely laws that say certain equipment had to “accept” interference from lawful transmissions. You’ll find a label to that effect on every piece of 802.11 and Bluetooth gear in the US, for starters.
>There’s definitely laws that say certain equipment had to “accept” interference from lawful transmissions. You’ll find a label to that effect on every piece of 802.11 and Bluetooth gear in the US, for starters.
If Boeing sold planes with altimeters that rely on frequencies that weren't allotted to aviation, then Boeing sold defective planes and should absolutely be responsible for retrofitting them. The fact that those frequencies are recently coming into use is immaterial.
It would be different if Boeing designed their altimeters to only depend on spectrum that was allocated for aviation, but then the FCC came along and carved the 5G spectrum out of the aviation spectrum after Boeing built its planes.
In any other broadcasting circumstance "It'll be hard to come up to the spec we should have been following for years" would not be an acceptable excuse. They have a huge chunk of spectrum with a very wide guard band.
If a TV station started leaking over another channel, you can bet that'd be shut down almost immediately, regardless of the cost to the station for putting up faulty broadcasting equipment.
Boeing should be required to fix their broken electronics. Sucks to suck.
Tv stations do leak into adjacent bands. They contribute to the noise floor. It’s just that your real tv station broadcasts at 10,000W or whatever so it drowns out the other noise.
When it comes to radar, they cannot increase the TX power and have to detect a lower RX power. Also since they are analog any interference manifests itself as a direct error.
It’s like saying you should never be able to hear a whisper from your neighbours house. Obviously you can limit the amount of loud noises coming from your neighbours. You can’t silence them completely.
> When it comes to radar, they cannot increase the TX power and have to detect a lower RX power.
other radar altimeters tolerate this just fine - it is a few specific models that have problems with rejecting signals that (according to design specifications) they should easily be able to reject.
> It’s like saying you should never be able to hear a whisper from your neighbours house
if local code says that a house should have noise insulation sufficient that a 100db noise source located at 30 meters away should produce no more than X noise level inside the house, and a 100db noise source at 60 meters away (twice the original specification) is still significantly greater than X - then yes, your house fails to meet code. It's defective.
nobody is blind to the problem of radio interference. Design specs for what level of noise needed to be tolerated were standardized in the 70s. That spec hasn't been reduced, actually it has been relaxed to over twice the original guardband specification, and certain altimeters still fail. They're defective, end of story.
Replace them with the models of radar altimeters which meet the original spec, done. They exist, it's not a universal problem, it's a few specific defective models of radar altimeters. Boeing just doesn't want to ground their fleet again, and the FAA is humoring them because of regulatory capture.
> rejecting signals that (according to design specifications) they should easily be able to reject
Please link to this specification. Because I've read the specification (TSO-C87), and it actually says nothing about required levels of interference rejection.
Should it? Probably. But neither the FCC nor the FAA wrote it in.
>If a TV station started leaking over another channel, you can bet that'd be shut down almost immediately, regardless of the cost to the station for putting up faulty broadcasting equipment.
Any leaking that happens is caused by the 5G transmitters in the case under consideration. You are confusing two issues. The issue here is that strong and close transmitters can not be properly blocked by some of the radar altimeters in use under the separation rules established by the FCC.
An important job of the FCC is separating TV transmitters that are close in frequency so that they do not cause problems. If you live next door to a TV transmitter you will have no hope of receiving signals on adjacent channels. That is because of the physical limitation of your receiver and has nothing to do with the transmitter leaking anything.
Airplanes have a lifespan, older ones are mostly retired, and the rest need their radios updated to modern standards anyway. Airplanes from the 1950s normally will last essentially forever, but modern airplanes are built with lighter materials that have the downside of metal fatigue from normal flexing and so they have to be retired after so many uses. (beware of this when flying backward country airlines, it isn't unheard of for a "retired" airplane to be put back into service in a backward country - Boeing thinks they should be retired, but their standards are conservative and so there is potentially a lot of life left in the air frame before it suddenly falls apart killing everyone on board)
Note, their are airplanes built today that don't have the metal fatigue issues - material selection is a complex process that each design needs to consider. I'm not sure what the 737 is made of.
The FCC allocated spectrum for radalts to use, then set aside an equivalent amount of spectrum (which is an insane amount of spectrum for a guard band, easily double what most uses get) above and below the radalts spectrum as guard bands that no one is allowed to use.
The guard bands ensure that if there is a little spill over from 5G (which there won’t be because modern radios are better than that), or if the radalts have crappy filtering on their front ends (which it seems they do). Then nothing bad will happen, because the guard bands give everyone lots of space for sloppy engineering (which Boeing seems to be abusing)
Boeing is not abusing anything - they just published a study on the models of altimeters that were sold with their planes, in specific configurations. Similar studies are performed by Airbus, Bombardier, Dassault, Cessna, etc. etc.
And FCC rules only specified transmission frequency of radar altimeters, and radio is analog and perfect filtering is close to impossible (especially with the kind of chirping signal radar altimeters use, where whole 200MHz of spectrum is spanned in single chirp)
Guard frequency (121.5) is different than "guard bands" in this context. Guard bands are, as was guessed, a frequency range at the edge of an allocation where no energy is /intentionally/ transmitted, and where received signal /should be/ disregarded. Basically it allows the reality of some frequency spillage to be accommodated between what would otherwise be adjacent frequency allocations.
This is not true. 5G uses spectrum way outside the band that RADAR altimeters are supposed to be using. Boeing had years to fix their shoddy RADAR equipment, and the fix now can be as simple as fitting a high-pass filter.
That's not true. I work in aviation and we've had a number of reports of radar altimeter interference during takeoff and landing near airports with the new 5G towers. Older aircraft are particularly effected.
Can you share these reports? How does interference exhibit itself?
It seems there a disagreement on factual truth which as another commenter pointed out could be resolved by say a YouTube video showing "here's a radar altimeter malfunctioning near a 5G antennae"
Also your comment seems inconsistent with the fact that the telcos delayed deployment of 5G towers near airports due to concerns about interference during takeoff and landing. So how can there be reports of interference from 5G tower if they haven't even been deployed there (edit: are these international reports)?
(I work on radar, this all feels like lawyers lawyering and techies blogging, but not engineers engineering)
I've also heard these reports from a couple of friends who are commercial pilots. At least one of them filed an ASAP safety report, but I don't know of any way for the public to query that database.
I don't know of any commercial pilot who is going to jeopardize their job and their certificate by filming a YouTube video while landing. There is literally no incentive for them to do so - there's formal channels to report these things (like ASAP, see above).
Also, while turning on the 5G towers near airports was temporarily delayed, it was only a short delay (two weeks). Those towers have already been turned on.
The best news I can find about reports of interference is from this Bloomberg article. As a airline consumer, I’m glad the airline industry is being cautious, but as a radar engineer, I can say there is very, very low SNR to these reports of reports:
“The reports have come in the form of radioed descriptions to air-traffic controllers as well as through more formal incident-reporting channels. The FAA often gathers unconfirmed reports of aviation incidents, such as drone sightings, even if they’re difficult to verify. At least some of the reports from pilots of possible interference have occurred at locations where the C-band broadcasts don’t exist, suggesting no connection with the service, said two people briefed on the issue.”
If 5G was using spectrum way outside the band that these altimeters are supposed to be using... then we wouldn't have this issue. Those 737s aren't new, they certainly had permission to use that spectrum for years and while they may have had years to fix their equipment, it's certainly not as trivial as "add a high pass filter".
Now, I do agree that this should have been caught 5-10 years ago, when the standard was being developed. Boeing's incompetence wouldn't surprise me, which is probably why we see "FAA says problems for Boeing in 5G" as the headline, instead of "Aircraft companies warn of interference in safety, navigation equipment, ask FCC to reconsider" as the headline, 5 years ago. Although, as noted in the article, it seems that the FAA has been warning about the conflict - I'm just surprised that the FCC would go ahead with 5G if they had been flagged early enough.
So here we are, the FCC, in its negligence, assigned conflicting portions of the spectrum, Boeing, in its incompetence, didn't catch it - and now it's a big mess.
They couldn't have warned folks about more than a year or so sooner than that, because the spectrum bands for 5G hadn't even been fully decided prior to it. (The public notice of band reconfiguration only got announced back in May 2019)
The aviation hardware was compliant with the FCC rules (transmitting only within 4.2-4.4 GHz). FCC didn't specify anything about received interference, and didn't apply any of the methods used elsewhere in the world to limit leaking by 5G towers in 3.8-4.0GHz range.
Well the whole point is they didn't have permission to use that spectrum. The interference the FAA is complaining about is explicitly outside of the radalt allocated spectrum.
FCC has allocated radalt's 200Mhz, with another 200Mhz guard on either side. If these devices are not properly filtering out frequencies outside of this massive 600Mhz range, those devices are faulty and should never have been certified by the FAA in the first place.
It's reasonable for the FCC to assume that spectrum users will not be affected by interference from so far outside their allocation.
> Those 737s aren't new, they certainly had permission to use that spectrum for years
This statement seems to be at odds with what many others in this thread are saying: that they were never approved to operate in this band. I don't know enough about this issue to know who is correct--do you happen to have a source for that since you are certain of it?
They never had permission to use the 5G spectrum, and in fact never did. The issue is that the filtering is so shoddy that signals more than 200MHz away from the band they are using can cause issues. The fault for that lies squarely on Boeing.
Why? They don't make the radar altimeters and multiple aircraft manufacturers are affected. Why is Boeing at fault for issues that (also) manifest themselves on Embraer and Airbus aircraft?
Boeing is ultimately responsible for every part that goes into their planes. They didn't manufacture the equipment, of course, but they signed off on it meeting their standards.
> Those 737s aren't new, they certainly had permission to use that spectrum
No they don’t, and never have. Hence the current shit show today.
Boeing got away with it because old users of the 5G spectrum where lower power satellite comms. Hilariously the oldest 737 model is unaffected by this issue, probably because Boeing actually let their engineers do good work back then, rather than forcing them to produce the sloppy crap they build today in the name of profit.
FCC is vastly more important for the US economy than the FAA. FCC covers Cellphones, Radar (Aircraft+Weather), WiFi, Bluetooth, Satellites (GPS+Weather+Communication, etc), Radio, CB, Emergency Services, TV etc all the way out to astronomy. Their mandate further covers interference from both electronic devices like vacuum cleaners and physical structures. Add it up and we are talking a huge chunk of the US economy directly or indirectly involved.
Further the FAA is extremely dependent on the FCC, being unable to detect or communicate with aircraft would make air traffic control nearly impossible. They would still be responsible for crash investigations, pilots, aircraft manufacturing etc, but in the worst cast the only way to fly safely would be under clear skies.
Executive Department Sub-Agencies and Bureaus has FAA.
Independent Agencies has FCC. What is and isn’t an independent agency is complicated but the EPA, NASA, FDIC, Federal Reserve System are independent as are less critical agencies like Institute of Museum and Library Services, Peace Corps, and Railroad Retirement Board.
I watched Downfall and I have to say that while they technically avoided lying about the actions of the EA302 crew, the storyline they presented doesn’t match the flight data recorder data.
Downfall says “the crew knew about the MCAS risk, figured out they had an MCAS fault, applied Boeing’s checklist response, and still the airplane crashed”. All four of those things are independent and true facts.
What is omitted (and readily available to the filmmakers) is that EA302’s thrust setting remained inappropriately high (94% N1, takeoff thrust), causing an excessive airspeed, causing the crew to be unable to return the stabilizer to a normal trim setting by hand after using the electric cutout, which led them to the (correct) conclusion that they should turn the electric stab trim back on and command aircraft-nose-up via the electric system, which they did. That means that they undid the checklist response. Then, after doing that successfully for a short period of time, they stopped commanding nose-up trim and left the stab trim powered up (contravening the checklist), allowing MCAS to continue to command the fatal nose down trim.
So they got dealt an emergency situation and the airplane crashed. Boeing has some blame here, but Downfall’s presentation of the events as the crew responding correctly with Boeing’s checklist would make most politicians blush and worry they’d be caught lying.
If you believe that MCAS caused the first and contributed to the second, like I do, then at what point does the FAA not step in?
You could say Gravity contributed I guess to both crashes, and Boeing is not responsible for that, but the difference here is that Boeing deliberately hid the existence of MCAS to the pilots to avoid simulator training.
I think it's fair to say that MCAS caused both crashes. I think it's inaccurate/unfair to present the EA302 crew as having executed flawlessly (as Downfall presents it). They had elements of excellent airmanship; they also had flaws in their execution of that flight which, if avoided, would have likely been enough to save the flight.
>When moneyed interests compete it becomes the same as their being no moneyed interests
No. That's very incorrect.
For example: Moneyed Interest #1 wants A & B, Moneyed Interest #2 wants A & Not-B. It's entirely possible that Not-A is a bad business model, but is also in the interest of the citizenry at large to have Not-A be law.
If I use 11/8 for private network addresses because it's easier than trying to keep everything in 10/8, and then DoD starts advertising those routes on the public internet, did the DoD bungle their rollout?
How is the FCC "captured"? They're out there making a killing on auctioning out these frequencies with massive guard bands and are extremely patient with legacy users of those frequencies.
In Europe there are Boeing 737s and 5G C band radio masts. I'm guessing the laws of physics are the same in Europe. So I'm confused. What are they doing differently there? Why don't the US do the same thing?
EU C-band rollouts are 200Mhz lower than in the US, making for almost twice as much gap between them. That said, EU is still starting to get worried [0] after some tests showed malfunctioning equipment can cause interference.
Issues with previously allocated spectrum and shoddy setup of mobile telephone spectrum in general leading to them needing more spectrum in 3-4GHz bands
We (Europeans) use other frequency bands for 5G: 700 MHz, 1.8, 2.1 and 2.7 GHz. That's comfortably far away from the 4.2 GHz band radio altimeters use.
Why the US decided to use 3.8 GHz for their 5G, only God knows.
The transmitters have FCC specs on how much power can leak outside of the band (It's called the band edge requirement). If the radar can't handle this out of band power transmission, then the FCC is on the line for writing a spec that isn't protecting the bands that they operate. It is unlikely this is the case given how far out of band this is.
No, the 5G transmitters are in their designated spec, and 200Mhz away from the altimeter frequencies. The problem is that the radio altimeters might not have proper filtering, which wasn't a problem in the past because the spectrum now allocated to 5G was not seeing much powerful transmissions.
The radio altimeters are fully up to spec, but the spec does not say enough about filtering out signals outside of the required band. This oversight in the spec was never much of an issue because of the aforementioned lack of usage in the spectrum before 5G.
While this should have been better studied before the spectrum was allocated, it's not really the fault of the FCC.
These radar altimeters have very wide front-ends, as as a result are highly susceptible to out-of-band emissions. The radars are allocated from 4.2 to 4.4 GHz, so the bottom edge of the radar altimeter band is 200 MHz above the top end of the 5G band in question (3.98 GHz).
The fact that these radar altimeters are susceptible to out-of-band interference that is literally further away in the spectrum than the width of their entire allocation is IMO an engineering failure. Yes, spectrum management (rightfully) tends to err on the side of not forcing the incumbents to make modifications to existing systems. However, better filtering would resolve this issue and it is shocking that the engineers who designed them didn't foresee that other services would eventually be allocated in adjacent bands. Avionics is often NRE dominated, they couldn't have sprung for a cavity filter? Or if that was too expensive, designed more headroom in the LNA before saturation and filtered the out of band signal with a crystal or SAW filter at IF? Rejecting out of band that far away is not rocket science.
I don't think it's unreasonable in this case to temporarily suspend the rollout and give the aviation industry a deadline to fix its radars, but it should only be temporary. Any other radio service would be told to take a hike if it keeled over due to out of band interference that far away.
This seems like Boeing trying to get the government to cover their butt because they did shoddy work on the altimeters. They were allocated spectrum for the equipment and then built a system that monopolized frequencies well outside of the allocated spectrum.
I completely agree that Boeing needs to issue a recall order on all affected hardware and provide a fix. This should be painful, it is basically punishment for trying to cut corners on safety equipment.
To add: if you ever read an FCC label on a device it says “must be able to accept harmful interference” or similar. So I’d argue the Boeing devices are the ones out of spec, should be immediately revoked as out of compliance by the FCC, and be done with it so the masses can enjoy 5G in peace.
I believe no agency should consider downstream effects of applying the law, to ensure fairness. Why should Boeing get a pass but say an out of compliance robotic lawnmower gets enforced?
That's the kind of label you put on a device that can fail safely from harmful interference, in SOHO setting. It totally does not apply to aviation systems, and FCC didn't apply any of the mitigations used elsewhere in the world when 5G deployment in 3.8-4.0GHz range was allowed (it's in limited use in UK, and with restrictions near airports in Japan)
Second, the FCC was already involved in their development and certification.
Third, these radars have been in operation for decades.
You are talking about thousands of planes that have to be modified to accommodate telcos. If anyone should pick up the tab for this it is Verizon and AT&T.
Who cares? The comment you are responding to says "they did shoddy work on the altimeters." That doesn't mean that Boeing built the altimeters.
They specced them, procured, inspected, installed and sold it with the whole airplane. If the pilots' chair collapses, that's shoddy work on part of Boeing, and nobody would talk about how they are just buying the chairs from someone. Same with the radio altimeters.
> Third, these radars have been in operation for decades.
Ok? Sometimes corners cut bite you in the backside only after decades.
There is one question which matters: Are the 5G towers transmitting on frequencies assigned to the use of radio altimeters or not? If they are they must stop. If the radio altimeters degrade or might degrade because of transmission outside of their assigned range and guard then they are faulty.
> Third, these radars have been in operation for decades. You are talking about thousands of planes that have to be modified to accommodate telcos.
Perhaps Boeing should have bid of the spectrum that their products depend on being unused.
This is essentially the government leasing out previously unused federal land for mineral extraction and a nearby rancher saying "it ruins my view," only with safety concerns added in.
They didn't cut corners at all - that's the thing.
The allocation of the spectrum is only for transmission, and the radar altimeters in question passed that spec. It says nothing about receive, and due to how radar altimeter works, it's much, much harder to filter out interfering signals from systems like 5G (5G in case of interference will just drop maximum data rate as it filters mismatched codes or incorrect checksums, radar altimeter might return incorrect altitude)
Unless the airlines are installing the altimeters themselves, it seems like Boeing is still the relevant company. If your car’s airbag has a malfunction, the car manufacturer does the recall even if the fault lies with the airbag manufacturer. Presumably Boeing would then go on to sue the altimeter manufacturer though.
Aviation doesn't work that way. Airlines have direct aftermarket relationships with all of the OEMs making the components on their airplanes. From a certification and warranty standpoint, Boeing is the design authority, and if there is an FAA mandated fix for 737 RAs, Boeing will have a role to play. Whether Boeing is responsible financially or logistically for the fix depends on the nature of the failure (is it limited to the component or is it a systems engineering issue) as well as the contracts Boeing has with their supply chain and their airline customers.
That doesn't seem to be practical. Maybe for some big parts like engine airlines have direct relationships but all parts including radar altimeters ?
An modern commercial plane has tens of thousands of suppliers supplying millions of parts. No airline [1] could even imagine to have the staff to manage OEM relationships with that many indirect suppliers. That is what you pay Boeing for.
If that was the case no airline could afford to buy more than 1 type of plane or certainly not more than one manufacturer, you would need to handle all the suppliers in the industry?! it would be incredibly inefficient to do this for them individually .
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[1] Maybe United , American or Delta could have that kind of staff, but given the airlines operating margins in the last 2-3 decades even that seems unlikely
Commercial aviation works the way it works regardless of whether you think its practical.
And you're grossly overstating how many suppliers are on a commercial aircraft. There are in total an average of 30 tier-1s on a modern airframe, and yes, airlines are expected to work with all of them. Radio Altimeters are typically made by avionics suppliers i.e. Collins, Thales, or Honeywell for Part-25 commercial airliners.
Even a private owner can effectively have (if not direct, then through agents) connections straight to OEMs, bypassing original airplane vendor.
There's a reason why the only time two airplanes are identical is when they roll from assembly line as part of the very same order with same spec, and never again.
They certainly certified them on the aircraft. If it means putting pressure on the subcontractor that actually built them or finding a suitable replacement then so be it.
It's Boeing's job to make sure that the altimeters they put into planes are fit for use. It doesn't matter if those altimeters are sourced from Boeing, General Electric, Uzbekistan, or the Moon - Boeing is the one who has to make sure they work. It's why they make the big bucks.
Boeing can argue with and sue their suppliers, but that's not a problem for anyone but them and their supplier.
The altimeters are operating within their frequency bands. They are operating as designed and certified. The 5G towers are the ones doing the flooding.
The 5G towers aren't putting significant signal outside of their allocated bands. This would be a very different story if they were spilling signal outside of their allocations.
From an engineering perspective, I would guess, as an avionics tech, back in the age of dinosaurs, these radio altimeters are probably of a very old simplistic design as to have dead simple and reliable electronics built with an absolute minimal number of parts. The carrier generation is probably just a crystal and an analogue multiplier with lots of phase noise and wide band so a similarly simplistic receiver can pick it up.
Yes and no. Many other countries are using C-Band, but often under slightly different conditions. Some countries licensed frequencies that stop significantly farther away from the spectrum used by radio altimeters. Some countries have mandated lower power levels for C-Band. Some countries have created larger exclusion areas around all airports (rather than the smaller, temporary exclusion areas around some airports in the US). Some countries have mandated a downward tilt for C-Band antenna panels (nationwide or in areas around airports) so that the transmissions aren't going go up as much (but a downward tilt also limits the transmission range which is bad for wireless carriers).
I think one of the big things in the US is that anything that makes C-Band harder to work with makes it hard for 2 of the 3 wireless carriers to compete. T-Mobile has a lot of 2.5GHz spectrum that it has been using to launch high-speed 5G services. Verizon and AT&T had been waiting for their C-Band spectrum to be usable to launch their high-speed 5G services. In Europe, if all carriers are facing the same restrictions, it's a level playing field. In the US, if Verizon and AT&T face restrictions that T-Mobile doesn't face (for most of its spectrum since it's 2.5GHz and not C-Band), that doesn't offer a level playing field.
I think it's also more contentious in the US because we have a much more suburban and rural population. Transmission distance is really important in the US because people expect to get modern services even in low-density areas. Verizon built its business on the idea that you should expect excellent wireless coverage even in places that have virtually no people.
I think another part of it is that the FAA is often very cautious and it seems like they didn't coordinate well with the FCC in voicing their concerns early on enough.
The FAA does have a web page on C-Band (https://www.faa.gov/5g) which is their official stance on the subject. They cite "Lower power levels, antennas adjusted to reduce potential interference to flights, different placement of antennas relative to airfields , and frequencies with a different proximity to frequencies used by aviation equipment" as reasons why the C-Band situation in the US is different from that in other countries. Is the FAA being too cautious? Maybe.
Ultimately, no one wants their business plans disrupted. Airlines don't want to see issues that delay landings. Verizon and AT&T don't want to see things that delay their ability to provide fast 5G service.
Yes. They knew the dangers but the telcos wanted frequency. So the FCC attempted to undermine the aviation industry group that actually knows how radar altimeters work.
Blancolirio covers this in several videos, although his take is more nuanced than mine.
Absolutely garbage reporting. The FAA / Boeing have no right to the frequencies in question. Even worse, they were given guard bands the size of their entire allocation which is ridiculous, and it still wasn't enough.
This entire thread seems to be about guard bands and filter roll off rate. But my question is: why does the altimeter blindly rely on received signal strength (basically: AM)? Surely it should correlate the received signal with the previously transmitted signal modulated with some PN sequence or some more fancy code? I'm an EE but not a radar expert, but I had the distinct impression going back decades that this is how radars work (at least military ones), among other reasons to thwart jamming. Fwiw feeding false returns to enemy radar has been a thing since 1939. Simply saying "oh there's a bit of noise, let me assume it's the ground talking" seems quite stupid even before the big bad 5G came along.
a large chunk of it likely boils down to "digital signal processing would have been a top-of-the-line military capability in 1970 when the aircraft were designed, and the onerous recertification process ensures that the cheapest outcome is always to just re-use the system and never mess with it". There's no incentive to mess with a working system, and a huge cost.
do remember we're talking about commercial aircraft where software updates are still deployed on 3.5" floppies.
it's difficult because obviously this is not a domain where "move fast and break things" is an option, I certainly see the benefits of a conservative engineering culture. But the 737 MAX situation already happened as a clever end-run around not being able to touch anything, and not being able to touch anything is more broadly killing general aviation (small aircraft). Extremely few aircraft have been certified since the 80s when the new regulations went into effect, it is very expensive and difficult. And at some point that boils down to encouraging "the wrong fix" or simply ignoring problems.
these aircraft have defective radar altimeters, they are unable to function properly with a guard band over twice the size of the original design spec. The other problem here is regulatory capture - these aircraft shouldn't be in the air at all with a radar altimeter that is so dangerously defective. The right fix isn't "just let aircraft manufacturers ignore certification requirements when it's convenient", it's to come up with a level of certification that promotes a culture of engineering safety, but basically the FAA is just letting boeing keep dangerous planes in the air because it would be a mess if they didn't.
> these aircraft shouldn't be in the air at all with a radar altimeter that is so dangerously defective
A radio altimeter is not required equipment for flight, nor does lack thereof make for a dangerous aircraft.
It is required for certain approaches used during periods of poor visibility. The FAA has correctly published NOTAMs and ADs prohibiting those approaches.
In this episode, AIN contributing editor Mark Huber explains the 5G C-band interference issue that can affect aircraft radar altimeters. He explains how we even got into this situation, why there is the potential for the 5G wireless networks at Verizon and AT&T to interfere with radar altimeters, what the FAA is currently doing to temporarily ease the problem, and what can be done long term to solve this issue.
So what kind of settlement do we anticipate as compensation to Verizon and AT&T for allowing them to bid and purchase spectrum and then not allowing them to capture value from that spectrum, post-purchase? Seems like a slam dunk for a hefty payout of some kind.
Yes. C-band and it's usage for 5G didn't just turn up yesterday. Even if they do get payouts they will just it to give every customer free Apple/Samsung stuff.
In "aviation time", they turned up yesterday. Allocations everywhere else either are further away from radar altimeter frequencies, or follow similar mitigations to those proposed by FAA... for the very reason that aviation world was involved from the get go. But FCC selling allocation all the way to 3.98GHz with no mitigations happened very recently, while there are still worries (that are being verified) that 400MHz guard band might be not enough in case of transmitter failure.
Here's the actual text, so it's only some of the 200's that are unaffected:
"Based on Boeing’s data, the FAA identified an additional hazard presented by 5G
C-Band interference on The Boeing Company Model 737-100, -200, -200C, -300, -400,
-500, -600, -700, -700C, -800, -900, and -900ER series airplanes, except for Model
737-200 and -200C series airplanes equipped with an SP-77 flight control system"
And the SP-77 does include a radio altimeter...apparently a nicely selective one.
which is the complete report you can read for yourself that the FAA based their "concerns" on.
But, if you read between the lines, or at least my read on it is...
The wireless telcos agreed to pay the Incumbent Earth station operators to vacate the spectrum, the Airlines are a little cash strapped after the pandemic lock down, so, they figured why not stick our hand out and see if we can get a little cash out of the telcos.
Just my take on it, but reading the RTCA doc, the whole thing is completely baseless.
But, having said that, here is something to consider, the primary concern raised by the RTCA is not so much the base stations themselves, which are far away and hence, not an interference source, it is the phones on the plane as it lands, which are much closer to the radar antenna which is in the ass end of the plane (the lowest point on take off and landing).
If a phone is on in the plane it will drag the call along, if you turn down the BTS's around the airport this compounds the problem because the dynamic power control of the phone will power up in an attempt to hold the connection. In Europe, they have been using this same spectrum for a long time with no problems, so in the U.S. we are doing the opposite and turning down BTS's near airports. So do the opposite of what works elsewhere in response that actually aggravates the exact problem being raised.
In other words, the best thing is to leave BTS's up near the airport so the phones, closer to the radar antenna, will not interfere, like what works in Europe, so the phones don't increase power. So, we are doing the opposite.
Can anyone find any sources indicating whether this interference has been tested or measured? The FCC decided to auction off the 5G spectrum for fast data usage almost 5 years ago, one would think there'd be a study or experiment or two since then.
Several months ago when the grumbling got loud, all the articles seemed to talk about "potential" interference, and despite the FAA having an $18 billion annual budget, and Boeing and Airbus and airlines having bigger budgets than that, and having almost 5 years notice, I got the distinct impression that no one had bothered to do any tests. But they took to the media to raise the alarm about "danger" instead.
I'm actually hoping to be proven wrong here - please point me to some experiments or test results!
Yes, the RTCA did a study back in 2020 which identified the interference from 5G towers was outside tolerance for the aircraft equipment:
"The extent of the RF interference is summarized by the worst-case exceedance of the safe interference limit of radar altimeters by expected 5G signals in the 3.7–3.98 GHz band: 14 dB for commercial transport airplanes, 48 dB for business, regional, and general aviation airplanes, and 45 dB for helicopters. Further, the impacts are not only limited to the intentional emissions from 5G systems in the 3.7–3.98 GHz band, but also the spurious emissions from such systems within the protected 4.2–4.4 GHz radar altimeter band directly. In this latter case, the worst-case exceedance of the safe interference limit is 28 dB for business, regional, and general aviation airplanes, and 12 dB for helicopters."
Overall it seems like the FCC was trying to be innovative, while the FAA's precaution in fact is the malaise that's been infecting all of US government: overapplication of the precautionary principle, that any risk, even if small an theoretical, is worth stopping change for (but not asymmetrically for motivating change).
When it comes to commercial air transport, you don't want the FAA to take a different approach to safety. Aviation works today because of its safety culture.
The only solution is to repair or replace the radio altimeters, right? The only question is, who is going to pay for it, right? The FAA could mandate that all aircraft with “faulty” radio altimeters are grounded until repaired or replaced. That would force the airlines to pay for the fix. Or, the government could offer to go halfsies on the fix since it was the FCC that allocated the 5g spectrum.
Anyone know what that interference would look like in a cockpit? Would it be immediately recognizable as something wholly inaccurate in the radio altimeter (or even no reading whatsoever) or is there the chance that it produces an ever so slightly different reading? The opposite, of course, being the far worse scenario.
As I understand (not a pilot but just interested in aviation), these altimeters are critical for use during low visibility landings, to determine when it may be safe to continue landing, or when they must abort landing (e.g. if they can't see the ground yet because of fog)
Being wholly inaccurate or no reading may be equally dangerous if it happens at the wrong time.
Right, and I think the FAA requires airliners to be capable of landing in IFR ("low visibility") conditions, which makes sense—you don't want trans-oceanic flights to crash because the weather abruptly got worse at their destination and they can only land when it's clear skies.
So "this altimeter may be inaccurate near 5G" means "this airliner may not be airworthy near 5G" which means airlines must ground those planes. It sounds like there are enough of them that it'd seriously affect air travel.
> So "this altimeter may be inaccurate near 5G" means "this airliner may not be airworthy near 5G" which means airlines must ground those planes.
No, they don't need to ground the planes.
There's different types of IFR approaches available to chose from, depending on equipment and how much visibility is reported. An inoperative radio altimeter means the aircraft couldn't land using the approaches for the lowest-visibility conditions, but doesn't mean they can't land under other less-severe IFR conditions.
In practice, this means the aircraft wouldn't even be dispatched if the weather forecast showed the destination's weather was below the aircraft's capabilities. They would also have enough fuel to divert to an alternate airport with better weather.
The idea they can have this type of interference low to the ground in a landing situation (when the reflected power is high) is a total failure on behalf of boeing. I can't even fully get my head around the physics that would get you an issue with even normal filtering, much less what once should be able to do on an airplane with high fixed costs and safety of life factors.
Amazing they can't do GPS as a cross check on indicated altitude over a terrain model.
GPS is incapable of getting even close to the resolution required from radar altimeter, and altitude ranging in GPS was always worse than its circular error probable in 2d - and the best accepted dynamic, unaided GPS deviation is big enough to show the same result between correct landing, missed landing, and a fiery crash.
The problem is that radar altimeter is very precise device that for best precision needs to use all of its 200MHz bandwidth on transmit. And there are no methods to recognize that as part of the return in its own 200MHz band (or in the guard band) a random CDMA-encoded signal radiated outside of allocated spectrum (happens) reflected of random crap around the airport and gets interpreted as valid data. This is an analog system where the analog characteristics are core to how it works, so the methods that allow tight channel spacing in communications tech do not work for radar altimeters
1. This isn't just a Boeing problem. Not only does the FAA have these concerns for other jets, they've also prohibited some other jets from landing at some airports in some conditions because of it.
2. Boeing doesn't get to decide to just cross check against GPS. The FAA has rules about the equipment that can be used for various types of landings.
> Amazing they can't do GPS as a cross check on indicated altitude over a terrain model.
I mean they could, but they skimped out on just getting a halfway decent filter for frequencies 200MHz away from their signals what are the odds they'd pay for that.
No, they really can't. At least not until GBAS is rolled out. GPS is notoriously unreliable for altitude data.
GPS altitude is used for LPV approaches, provided you also have a WAAS correction signal, but those require higher weather minimums than the Cat II/III approaches that you'd use a radio altimeter for.
These altimeters are required for decreased ILS minimums and autoland. You can perform a Cat I ILS down to 200' AGL in 1/2-mile visibility just fine without any radar altimeters.
Am a pilot, but just PPL, from my understanding the greatest threat is forcing the autopilot to perform certain maneuvers thinking terrain is closer than it actually is.
The altimeters are used by the auto pilot, especially in bad weather. In the cockpit the altimeter would probably give obviously false readings, but in that case the plane can't land and has to divert. It is possible the interference could cause the radar to give a plausible but incorrect reading, but this is a worst case and to my (limited!) understanding, remote possibility.
The meta of it is that some time ago, it was decided that just letting the FCC manage spectrum allocations, as they have since 1934, wasn't good enough. The decision was made to "sell" chunks of the spectrum for exclusive lease for various chunks of time and geography.
This was a horrible decision, because those fees are, in effect, a tax, that will inevitably be passed on to the users.
On top of that, it provided the incentive to take what was a reasonable separation that protected aircraft navigation bands from other users, and sell that space off.
On top of that, the FCC/FAA didn't bother letting the rest of the world know this was going to happen, even though they had YEARS to do so.
Thus, the current mess. Signals are popping up where the equipment currently in use was never expected to tolerate them. It's putting lives in danger.
I'm no expert, but why can't we just add some regulation that says the insurance carriers will be responsible for any liability beyond 2024 (or whatever) and that they're free to charge whatever they want based on the make and model of the altimeter in use on the plane?
Why not make something safe instead of trying to end run an economic incentive to safety? Airplanes are one of the safest per mile form of transportation in the US because we regulate the actual safe flight instead of playing economic games to get companies to act safely.
I'm suggesting this may be a viable alternative given that this has been a known potential issue for quite some time now and the aviation industry appears to be dragging their feet on replacing the faulty gear. It seems to me premiums that approach or exceed the cost of an upgrade would encourage them to get moving on the fix.
On the other hand, maybe it makes more sense for insurance carriers to simply refuse to assume liability for flights on airplanes with altimeters that are known to have issues with 5G tech. That approach seems to work for discouraging new construction in floodplains.
Insurance is generally a reverse-looking science and does a really bad job at proactively measuring risk.
You save more lives by having an engineer analyze potential problems with the plane before it crashes, than you do by waiting for one to crash so an actuary can count it.
I see a lot people blaming boeing here? These sensors radar sensors were made before even the FCC allocated the 5G spectrum.
Let's also not forget 5G equipment will emit outside of its assigned spectrum even with a buffer zone between frequencies. Especially when you consider the harmonics. Now each order of harmonic gets weaker from primary frequency.
As for these altimeter sensors anyone have a datasheet for them? Quite curious what the recommended noise floor for these are?
All equipment can emit outside the allocated frequencies, which is why you have band pass filters .
FAA is really the problem not Boeing, like any company they only did the bare minimum required to get certification .
Had FAA they mandated stronger specs initially or at-least forced Boeing to upgrade in the last 10 years this was being discussed and allocated, this won't be a problem. That will be expensive for Airlines(grounding loss of revenue) and Boeing (recall,certification and upgrade) nobody wants to foot the bill so FAA kept delaying .
Time and again we have seen FAA favor the industry even at the cost of lives (like with 737-MAX grounding) so this is not all that surprising from them
We are talking about radar here the receiver will be receiving weak signals that are reflected. They may also have slight shifting in frequency due to reflection and the doppler effect. The noise floor is much lower for radar than communications. A radar receiver also will generally read a wider frequency band than communications. 200Mhz between frequency bands may seem like a lot for communication purposes, but that is not necessarily true for radar.
Also you can't make a perfect band pass filter, also for radar the band your going to be filtering is gonna be wider to begin with. Also all transmitters will emit higher order harmonics of the primary frequency, if the broadcast power is high enough those harmonics could very well be above the noise floor of other frequencies.
There are altimeters which already are being used including by Boeing which perfectly pass the required specs. Nobody including FAA / Boieng are claiming technically it is impossible or will take very long to develop.
The FAA is only calling out 737s after clearing them in this statement . They had said on 20th Jan "Airplane models with one of the 13 cleared altimeters including all Boeing 717, 737, 747, 757, 767, 777, 787, MD-10/-11; all Airbus A300, A310, A319, A320, A330, A340, A350 and A380 models" [1] and now backtracking
They had adequate time to plan and roll it out to affected planes and they have not for the same reason telecom and FTC are upset -- money . Airlines/Boeing/ FAA do not want to foot the bill of this upgrade. Telecom companies spent $70 Billion on the spectrum and delays are costing them so they are upset.
All of those altimeters are up to spec. It's just that the spec never included "must magically filter out high power leakage from 5G towers that won't exist for 30 years", and making a filter for radar altimeter is much, much harder than for telecommunication equipment.
It has nothing to do with whether they were up to spec originally and now don't because telecom did something.
FAA on Jan 20th of this year made a statement saying all these planes were approved to use under current new conditions for 5G. Now have since rolled back that for 747s(on Jan 25th) and 737s(23 Feb/27th Jan). Read their statements linked carefully again.
It tells FAA is not competently handling the situation. First they are caught totally unprepared for the 5G rollout after having years of notice, then issue approvals and are rolling back said approvals. At this point I am not inclined to believe they know what they are talking about at all.
New data invalidating old data happens all the time in aviation, and they have to deal with increasing number of 5G transmitter models operating in new environments. It's not something you can do easily.
In fact, apparently issues started cropping up with 400MHz guard band used in most of europe, when the towers malfunction.
This issue hits ALL PLANES that use standard frequency radar altimeters. Including Airbus, Bombardier, Cessna, Learjet, Dassault, etc.
What happened is that aside from trying to put limits on transmission characteristics for C-band near airports, there is a concerted action to verify how the many different models of radar altimeters interact with 5G interference. This is a report on configurations sold by Boeing, from Boeing, as they went over all configurations they've sold of specific types.
Boeing’s receivers are picking up radio signals well outside the band allocated to radio altimeters - they got away with this until now because the nearby bands were unused.
From my understanding, Boeing's radars will receive a much wider band than Airbus', combined with most other countries allocating 5G spectrum further away from the expected radar frequencies. They could switch but it would involve massive effort and possible recertification of the airframes.
Boeing and Airbus (and others) buy radar altimeters from the same vendors.
It just happens that Boeing finished checking out a bunch of configurations that they have sold in the past against interference from 5G under FCC allocation (AFAIK they previously checked against setups allowed in other countries), and published results.
Airbus and others are also performing extra tests now.
CTIA is a lobbyist organization, whereas the technical assessment done by the aviation industry was done by a research consortium. The aviation industry has produced data to show 5G is a problem. What data has CTIA shared to prove that it's safe? To date, they haven't shared any.
Anyone know the radar altimeter make and model? I can't seem to find anything when I do a search. All that pops up is the aircraft model number. Aren't the altimeters manufactured by companies like Honeywell. There should be a datasheet on the model available somewhere
It's not that it's particularly useful so much as it's available. The FCC has been clearing spectrum because more spectrum means that carriers can offer faster 5G services. Mid-band spectrum (in the 2.5-6GHz range) is particularly useful because it offers a good combination of range (measured in miles) while still having a decent amount of spectrum available and the possibility of things light higher-order MIMO to offer capacity gains.
Millimeter-wave spectrum (in the 20-50GHz range) has lots of spectrum available, but its range is often in the 50-300 foot range. It's also important to realize that because we're talking about a radius, when we turn that into a circle the difference gets magnified. A 1 mile range means covering 88M square feet. A 100 foot range means covering 31,000 square feet. 53x more range turns into 2,800x more area covered.
Initial 5G networks in the US often used 5-20MHz of low-band spectrum (below 1GHz). This does have some utility as 5G NR is marginally more efficient, even in low-band spectrum. However, deploying with 100-200MHz of mid-band spectrum offers the kind of huge gains that offer 10x (or even more) data speeds.
There isn't really a lot of spectrum that hasn't been allocated so it's often a game of figuring out who you can move for the least cost and most benefit. They chose to move C-Band satellite operators (at a cost of billions). Previously, the FCC freed up spectrum in the 600MHz range by having TV broadcasters relocate from UHF channels above 37 to lower channels.
Why do we even need 5G it seems like there’s always something, whether real or tinfoil, risks and unknown risks, so at one point do we decide that what we have is good enough?
Is there not any room in the regulatory world for “better safe than sorry”? At some point we could maybe just stop adding new energy waves to the sky.
It’s like the Wi-Fi router thing, it’s to the point where I’m going to need to buy a big piece of land to live on just so I don’t have 50 different Wi-Fi networks bombarding my house 24/7. I mean they say it’s safe to have a Wi-Fi router but did they study having 50 at once?
Wifi signal drops off with the square of your distance from the radio. So if you feel safe sitting 5 feet from your own router, you're only getting 1/25th as much signal from your neighbor's router 25 feet away (well, almost certainly less since it's going through walls, windows, etc). (some factors can change this, like if he has a high gain directional antenna pointed directly at you, you could see more power from his router than from your own)
So unless you're sitting in a Wifi router store surrounded by wifi routers, you're not getting irradiated by 50X more power even if your computer can see 50 wifi networks around you.
> Why do we even need 5G it seems like there’s always something, whether real or tinfoil, risks and unknown risks, so at one point do we decide that what we have is good enough?
Because it consists of non-ionizing EM waves, the risks of which are very well understood.
And if you're concerned about the amount of non-ionizing EM waves in your environment from these 50 wi-fi networks, you should never go outside, since the sun is constantly blasting you with ~1,000,0000 GHZ-frequency electromagnetic waves, at an energy flux of ~1300 watts/square meter. It's half a dozen orders of magnitude more[1] energy than those fifty wi-fi networks are putting out. They aren't even a rounding error.
The only thing the 5G 'controversy' reveals is that the public is happy to listen to people who don't know anything, as long as they are being told what they want to hear.
[1] Not just more energy, more dangerous energy. Solar radiation, unlike 5G, is actually ionizing. Those radiation waves carry enough energy to break molecular bonds in your body.
While I don’t think the paranoia around 5G is justified, this isn’t an appropriate comparison.
Humans have a barrier, known as the “skin”, that’s designed to block the electromagnetic radiation from the sun and repair the damage it causes. Many of us even have an extra protective compound in us known as “melanin”. Nevertheless, damage to this barrier from the sun is responsible for causing many cases of cancer and people often wear protective compounds, known as “sunscreen”, to reduce cancer risks by blocking out the most dangerous ionizing radiation.
It is more subtle than that. There are various protein molecules that vibrate inside the cells as a part of their normal functions including those responsible for immune system functions. As such there are absorption spectra due to resonance with vibration frequencies. This was mostly ignored in past, but there are speculations that 5-5O GHz radiation can be absorbed affecting molecular functions with unknown consequences.
I don't understand how they could conclude that their sleeping caps had any effect when they apparently went into the study with the belief that they work and decided not to have a placebo control group because it would be unethical.
As these patients were all ill, many undergoing olmesartan treatment with therapeutic intent, we decided that ethical considerations precluded the distribution of “placebo caps” without the silver threads.
And they were apparently distributed to those that requested them, likely those that already thought they would work:
Sleeping caps” were sewn and, upon informed request, distributed free of charge to members of our follow-up olmesartan cohort.
"A case series of 64 patient-reported outcomes subsequent to use of a silver-threaded cap designed to protect the brain and brain stem from microwave Electrosmog resulted in 90 % reporting “definite” or “strong” changes in their disease symptoms."
(edit: in case it isn't clear, this is not how you science)
Well, you have asked for it and I wrote initially “speculations” without citing this. The idea that complex protein molecules may absorb 5-50 GHz radiation via proposed mechanism in the paper is at least plausible and the calculations from the paper does not look like totally unsound. So this should be investigated.
Because smartphone sales have leveled off and consumers are content holding onto their devices longer.
Manufacturers and telcos have become addicted to the 1-2 year device renewal cycle and want it back. Thus the marketing department instills “5G” as a need in the mind of the consumer.
Also, for people on metered plans, it behooves the telco to develop means for you to exhaust your quota as quickly as possible to get you into overages (and subsequently onto a pricey unlimited plan).
Everyone complains about the lack of choice and competition and quality among internet service providers (ISPs.) 5G is fast enough that you can use it to replace your wired internet, just as cell phones displaced "land lines" over the past two decades. 5G, and hopefully Starlink, will be ISP game changers.
Very anecdotal, but a flight my wife was on 3 weeks ago returned to the terminal before takeoff and had to switch planes because of an altimeter malfunction. The pilot cited it was because people didn’t turn off airplane mode.
The Boeing 737 design was introduced 50+ years ago and is still used (albeit not in 50 year old planes) today in a multitude of airlines for passenger travel.
That said the 737 MAX fuckup is something that neither Boeing, or the many worldwide air travel regulatory institutions should be forgiven for. But that doesn't make the 737 design itself bad. That particular iteration, due to Boeing's attempt undertake Airbus and falsely sell the planes to airlines as a drop in replacement with zero extra training needed unfortunately resulted in deadly crashes. The people that decided on that should be charged on the deaths that occured because of their greediness.
> The people that decided on that should be charged on the deaths that occured because of their greediness
For whom should the buck stop? Boeing, who designed the upgrade with lower carrier costs in mind? The carriers who bought and flew a compromised flight program in order to offer lower ticket costs? The passengers who choose a carrier based on cost instead of quality?
Ok, I got a little carried away there. From what I understood from reading the reports on the various crashes, (I don't have a background in aviation so take this with a gigantic pair of tweezers) the crashes could have been prevented by simply informing, and briefly training the pilots with the newly introduced systems that corrected the pitch of the nose to compensate for the change in engines while maintaining the same body. But instead of doing that from the start, Boeing marketed the plane to airlines as a drop in replacement for their old 737 fleet where the pilots would need no extra training as it should behave "exactly the same" as the old one.
Whoever decided on that should be mainly responsable for this. Of course the passengers don't have the fault and the airline would be at fault only if they continued using the decommissioned planes that were known to be unsafe. I'm not mistaken issues have been mitigates and those planes are in use in many areas of the world now.
There's nothing wrong with designing an upgrade with lower carrier costs in mind, but any potencial differences on how the plane behaves should always be informed, even if a computer is supposed to correct for it.
It is not a matter of simple pilot training. It turned out pilots had only 10 seconds to disable the system after that it would be too late. This is exactly what happened at the second crash. The disable switch was pushed but it was not possible to recover.
I believe they would have been able to recover had they cut the throttle and let the airspeed reduce to the point that they could manually trim the aircraft.
Hard to blame them though - while it was definitely pilot error when they got stuck focusing on trying to fix the elevator trim issue and neglected to heed the overspend warning and take the aircraft out of military power, this issue was no doubt precipitated by the lack of proper information that Boeing had provided to pilots regarding the functioning of the MCAS system.
..The 737 MAX's larger CFM LEAP-1B engines are fitted farther forward and higher up than in previous models. The aerodynamic effect of its nacelles contributes to the aircraft's tendency to pitch up at high angles of attack (AOA). The MCAS is intended to compensate in such cases..
..MCAS was supposed to compensate for an excessive nose up angle by adjusting horizontal stabilizer before the aircraft would potentially stall..
..MCAS played a role in both accidents, when it acted on false data from a single angle of attack (AoA) sensor..
..elected to not describe it in the flight manual or in training materials, based on the fundamental design philosophy of retaining commonality with the 737NG..
..thus minimizing the need for significant pilot retraining..
..Thus, airlines can save money by employing and training one pool of pilots to fly both variants of the Boeing 737 interchangeably..
..As an automated corrective measure, the MCAS was given full authority to bring the aircraft nose down, and could not be overridden by pilot resistance against the control wheel as on previous versions of the 737..
- Fixing a problem (engine size/placement not analysed) with a more complex solution (MCAS).
- Acting on only 1 sensor.
- Not described in manuals.
- Not able to override.
Text-book red flags. Definitely greedy managers that pushed towards this. However the engineers involved must have a bad taste (at Boeing and FAA). Engineers should take an oath like doctors do "Hippocratic Oath". The relationsship between business and engineering must be strictly defined. Compromises has to be taken, even in safety critical systems, but when taken it can't be the same business that can assess it OK. Engineers must be able to say categorically no and have it recorded outside business, without fear of losing jobs.
Most 737s are among the safest planes ever built (because they aren't MAX). Whether or not the MAX will live up to the safety record of the previous gen going forward is yet to be seen.
Going forward? You don't get to wipe off a chunk of the graph that you don't like, the crashes that happened and the flights that happened without crashes are all part of the MAX safety record (oh, and that goes for the 'rebranded' version as well).
No one is wiping. By “going forward” I mean that if the corrections prove working then for each flight hour the safety record improves in the sense of accidents per flight hour.
The MAX safety record is terrible because there are many incidents per flight hour. Not because there are many incidents.
It needs to fly about 10M flights per fatal accident to be catching up with the 737 NG.
That's still to be determined. They're approved for low-visibility landings at fewer airports than any other passenger jet (including the 737), according to this: https://www.faa.gov/5g
But, let's not compare apples and oranges. Concerns about safety doesn't kill people, it protects them. The 737NG has a very low accident rate, and if you're looking for a plane with a statically lower incident rate, the ERJ is your only other clear choice. This is regardless of the fact that the FAA only allows ERJs to land in low-visibility at 3/4 of US airports.
The A320's cabin is several inches wider, so it feels more spacious, and the windows are higher, which also makes it feel less claustrophobic. The extra width also tends to translate into slightly wider seats and/or a wider aisle, because when I fly economy class, both 737s and A320s tend to be configured with 3 seats on either side of the aisle.
On the other hand for tall people (which I am not) who use window seats (which I don't), the A320 is worse though because the cabin wall curves in more at head level.
If anyone cares how this is impacting aviation rather than the likely more appropriate debate of if this should impact aviation... It stops an airplane from landing in a 93 foot range of weather, if the clouds are between 107 feet and 200 feet above the runway (okay at one airport for one approach for one runway - but it's likely +- 50' true at most places, see below).
In bad weather certain aircraft rely on their radar altimeter to help guide them to the runway. It gives them an altitude they can use to decide to abort their approach that is more accurate than air pressure combined with their inertial system. This below link shows that within a given distance of 5G they are not allowed to rely on their radar altimeter for those approaches.
> When operating in U.S. airspace, the following operations requiring radio altimeter are prohibited in the presence of 5G C-Band wireless broadband interference
> Instrument Landing System (ILS) Instrument Approach Procedures (IAP) SA CAT I, SA CAT II, CAT II, and CAT III
Below is the link for the S-ILS RWY 36 for DFW that requires SA CAT II. At the bottom you can see "RA 107/12" which means the airplane can fly down to 107' on RA (Radar Altimeter) without seeing the runway. At 107', if they don't see the runway environment, they must abort the approach. This approach assumes a working Radar Altimeter. The 5G NOTAMS effect this approach.
Below is the NOTAM for DFW affecting approaches. With this NOTAM an aircraft cannot execute the above approach, so if the weather is between 107' and 200' (the minimum for a regular ILS without RA), then they are not allowed to land at that airport - where before the 5G NOTAM they could.
This is the narrow band of bad weather conditions in which the 5G affects approaches at DFW for that runway, 93 feet.
In the NOTAM you will see the above approach "ILS RWY 36L (SA CAT II)" listed and "PROCEDURE NA [not available] EXC [except] FOR ACFT [aircraft] USING APPROVED ALTERNATIVE METHODS OF COMPLIANCE DUE TO 5G C-BAND INTERFERENCE PLUS SEE AIRWORTHINESS DIRECTIVES"
> FDC 2/3758 (A0495/22) - IAP DALLAS-FORT WORTH INTL, DALLAS-FORT WORTH, TX. ILS RWY 17C (SA CAT I), AMDT 11B ... ILS RWY 17L (SA CAT I), AMDT 7 ... ILS RWY 18R (SA CAT I), AMDT 8A ... ILS RWY 35C (SA CAT I), AMDT 3 ... ILS RWY 35R (SA CAT I), AMDT 4B ... ILS RWY 13R (SA CAT I - II), AMDT 9B ... ILS RWY 17R (SA CAT I - II), AMDT 23D ... ILS RWY 18L (SA CAT I - II), AMDT 3 ... ILS RWY 31R (SA CAT I - II), AMDT 15 ... ILS RWY 17C (CAT II - III), AMDT 11B ... ILS RWY 17L (CAT II - III), AMDT 7 ... ILS RWY 18R (CAT II - III), AMDT 8A ... ILS RWY 35C (CAT II - III), AMDT 3 ... ILS RWY 35R (CAT II - III), AMDT 4B ... ILS RWY 36L (SA CAT II), AMDT 4 ... PROCEDURE NA EXC FOR ACFT USING APPROVED ALTERNATIVE METHODS OF COMPLIANCE DUE TO 5G C-BAND INTERFERENCE PLUS SEE AIRWORTHINESS DIRECTIVES 2021-23-12, 2021-23-13. 19 JAN 05:00 2022 UNTIL 19 JAN 05:04 2024 ESTIMATED. CREATED: 13 JAN 05:05 2022
- 5G is bad because it is a Chinese tech and they can spy on us
to
- it interfere with our equipments
Looks like they learn, instead of admitting they are behind china in telecommunication tech, they now push the idea that it just is making our "old btw" tech unusable
""5G interference could adversely affect the ability of aircraft to safely operate," said the bosses of Boeing and Airbus Americas, Dave Calhoun and Jeffrey Knittel, in a joint letter to US Transportation Secretary Pete Buttigieg.
""Airbus and Boeing have been working with other aviation industry stakeholders in the US to understand potential 5G interference with radio altimeters," Airbus said in a statement."
The article body and headline are (of course) at odds IMO. The headline is very much "doomscroll" material while the article points out that interference could basically manifest as having to rely on secondary systems and protocols to land. If I'm missing something then happy to be corrected :D
Airline accidents almost never have a single cause. It requires multiple failures to align before you have disaster. Malfunctioning radio altimeters could be one of those factors.
That said, this is Boeing's fault. They need to clean up their act ASAP, and it seems like they've been banking on the FCC covering up their mess and are now running around with their hair on fire.
A reasonable stopgap may be to simply not allow 5G towers to use the frequencies ranges in question within some radius of an airport (20 miles?) for a few years until Boeing fixes the problem.
A 20 mile radius of any airport likely covers a significant portion (60-70%) of all urban/suburban population. They might as well just give up on that spectrum at that point.
Maybe, dare I say, Boeing should go back to following the spectrum guidance. Is it going to move to the THz channel next and start complaining about visible light?
I would flip their argument on its head and state that as altimeters are that critical, make sure they follow the spec to the letter.
It's, like other commenters said, as if your neighbour sends you an eviction notice for your own house because you are next to him.
5G has taken a tremendous amount of effort and multiple years of work -- people have spent a decade on this. Boeing decided to not follow the spec. I think I will switch to Airbus. ;)
tl;dr: if Boeing can not keep inside a spectrum for the altimeter what else have they "cheated on?"
Airbus has the same issue. So does Bombardier. So does Dassault.
Using the eviction notice metaphor , this is a developer building a stadium with sound system rocking your walls every night, because someone sold them a parcel too close for noise abatement.
Could you please (I am asking out of curiosity) provide information about other companies? All I find are about passed tests.
Your example metaphor is good I agree! The developer of the stadium here are the radio altimeters' manufacturer in question.
The 200 Mhz gap between bands had been known. They just didn't want to: a) fix their leakage b) buy the "neighborhood" ie the band.
They had multiple chances over more than 10 years now. And now they use the FAA to bail them out.
We have the expectation, especially whoever flies and uses altimeters directly, that they will be extremely robust. From what I have seen so far a lot of corners have been cut.
P.S. Wouldn't you double think before flying with some equipment that your undergraduate self (EE) would design better? Pay for more band, not with our lives.
Except it wasn't 10 years for the US' C-band, and for all the world outside of USA there was bidirectional cooperation.
If we keep to the stadium metaphor and you want to use radar altimeter as the stadium... 5G is someone deciding to build a house after it's been known for decades that the stadium is there then deciding to complain about noise.
The radar altimeters are not the ones leaking, and no corners have been cut in fact. It's effectively "spec was changed without coordination, and now we have to do extra tests to verify that it's safe"
Nobody raised a flag then. And nobody tried to stop the auctions. FCC has full jurisdiction on this. The C band is the popular one as the article also stresses. Yes FAA complained in 2020 and tried to delay the auction.
To even get to the auction the 5G workgroup has been simulating these ranges since 2014 at least (from personal knowledge). There is no chance the engineers working in the neighborhood bands did not know as at least word of mouth was out for anyone doing RF, WiFi, or with interference channels.
If you look at the 2016 European 5G annual journal the 3.5Ghz area is mentioned. https://5g-ppp.eu/annual-journal/
(The bands 42 and 43 which are the ones on question where mentioned that is.)
In 2017 FCC did the RFC for the auction. This is the biggest auction ever. Aviation Spectrum Resources (ASRI) was testing and passing altimeters (initial test done and submitted 2019). FAA and various altimeter developers did nothing. (See https://5gamericas.org/wp-content/uploads/2021/07/Mid-Band-S...)
If you see the article I shared in prior post, FAA has approved radio altimeter models and has disproved others.
In 2011 there was an assessment of the neighborhood bands interference as part of what they called NTIA Fast Track evaluation. And they raised interference issues with current spectrum and practices. FAA and developers did nothing.
FAA needs to pay to properly deploy antennas like other countries have for years, in airports and/or have someone buy the spectrum. 40 countries did it right already.
Worst case, they had since 2011 to do this.
P.S. When you build and antenna/receiver you are the one responsible for staying in spectrum.
There is 200 mhz fallow. You can't just go around building devices that will get affected even with a 200 MHz buffer. Nobody is invading their spectrum.
Sorry to rant, but... I drives me nuts when people use "could" in this context.
5G has been in development for over a decade I think. It's been deployed in the real world since 2019. So what the fuck have the FAA and FCC been doing in that time? You would have thought someone would have actually determined whether 5G can interfere with one of the most popular commercial aircraft?
Really? No one checked? No one asked?
This has been a mainstream news story for 4 weeks.
And no one at the FAA or FCC has put a 5G antenna next to an 737 and even tried check? No one has put together pilots logs or looked at aircraft systems logs? And in that time presumably 100s of 737s have taken off and landed and flown over these?
At this point, we know 2 things: It's very unlikely this an issue or we'd have seen a lot of serious incidents probably including an actual crash AND we need a federal organisation that manages aircraft safety and another for communications including EM spectrum to avoid inference and we don't actually seem to have either.
I work with trading tech. Nothing complex or amazing. Just money, nothing safety critical. Sometimes things break or we have bugs. I can say a lot of things to my boss when something goes wrong, I can't say "It could be a massive problem, but I haven't bothered checking despite having 4 weeks to at least start" so I don't really know.
"They couldn't have warned folks about more than a year or so sooner than that, because the spectrum bands for 5G hadn't even been fully decided prior to it. (The public notice of band reconfiguration only got announced back in May 2019)"
It's not that easy to exhaustively test that the many different 5G systems won't accidentally corrupt radio altimeter signals. It's been in the works for a long time, and aviation and telecom groups have cooperated on this worldwide.
It's why everywhere else, there are either mitigations on 3.8-4.0GHz frequency use near airports, or the spectrum is not allocated to 5G comms.
Then, quite recently in the whole development, FCC decided to allocate 3.8-3.98GHz to telcos, without mitigations near airports
I see their statements as indicating that they do know in fact there are failure modes that will occur some of the time. When you use could in this context, it's to indicate that it won't happen in all circumstances, not that you don't know if it can happen at all.
That's what gets me: they don't seem to know. Or at least they don't want to say?
If they know there is an (intermittent, occasional) issue then ground the planes. Don't announce it, but cryptically and then do nothing and wait for a few 100 deaths.
If they know there isn't a problem then shut up.
And if they don't know, why the fuck don't they know after (at least) 4 weeks of testing. Can't they at least say all tests fine or 99% of tests fine or we crashed 4 planes but maybe the test pilots were just bad?
Am I missing something?
If a rancher buys a plot of land from 34.42°N to 34.44°N to graze his cattle on, but in actual fact grazes his cattle all the way from 34.37°N to 34.47°N. Then a farmer buys a plot of land from 34.37°N to 34.398°N to grow wheat on. Does the rancher still get to herd his cattle down to 34.39°N to feed his cattle? The cattle have to eat, after all, and cutting down the grazing land by 30% could cause some cattle to starve to death. And the rancher has a vested financial interest in ensuring his cattle are well fed, and that wheat is good eating. And the rancher has always been grazing his cattle there, what right does the farmer have to till the soil on the racher's grazing land? And we, the American public, have the right to buy beef. Why should the farmer purchasing 34.37°N to 34.398°N interfere with my ability to buy a steak?
Does any of this make any sense to anyone?
Unless there's additional information I'm unaware of, it seems as if the design and/or manufacture of the radar altimeter is not fit for purpose. Using 3.7GHz to 3.98GHz for 5G doesn't break the radar altimeters; the radar altimeters are already broken and must be fixed or grounded, because the equipment is broken and unsafe.
If 5G equipment is emitting outside of its allocated 3.7-3.98GHz spectrum then the FCC needs to drop a brick on that of course.