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Ask HN: Are mobile phones on a plane taking off or landing really dangerous?
52 points by rakkhi on Sept 27, 2010 | hide | past | favorite | 129 comments
Are there any actual studies and detailed research with proof that having my mobile phone on during take off or landing provides and increased risk of the plane crashing (or other adverse reaction?)

I mean logically if planes did not have sufficient shielding for this would a terrorist not just bring about 1000 phones (say its for export for sale) as hand luggage and just leave them on? Also some planes now now allow mobile phones to be used on board.

Things that have been done for the sake of it or have continued because that was the way it has always been really annoy me. And I really hate having to switch off my phone and my RSS reader getting dirty looks for fellow passengers.

From the press release for a Carnegie Mellon study in 2006:

"We found that the risk posed by these portable devices is higher than previously believed," said Bill Strauss, who recently completed his Ph.D. in EPP at Carnegie Mellon. "These devices can disrupt normal operation of key cockpit instruments, especially Global Positioning System (GPS) receivers, which are increasingly vital for safe landings." Strauss is an expert in aircraft electromagnetic compatibility at the Naval Air Warfare Center in Patuxent River, Md.


It's true that no crashes have been positively linked to cell phone use, but it's also true that black box recorders don't measure RF interference so it would be difficult to do so.

edit: and here's a link to the whole paper http://spectrum.ieee.org/aerospace/aviation/unsafe-at-any-ai...

In one telling incident, a flight crew stated that a 30-degree navigation error was immediately corrected after a passenger turned off a DVD player and that the error reoccurred when the curious crew asked the passenger to switch the player on again.

Seems like GPS for landing is poor dependency, considering how easy it is to jam GPS...

That's why RNAV (GPS) approaches are still not allowed (for commercial flights) AFAIK.

30 degree error has nothing to do with GPS though. Probably DVD player interfered with Localizer signal.

GPS approaches are allowed, FWIW.

I'm also not sure the localiser signal was involved since I don't think the crew would have gone to the back to get the passenger to mess around with the DVD during an approach.

Could be a magnetometer too -- they are very touchy. Although you'd think it would be far away from the passengers.

I flew for the airlines.

The problem is not your everyday takeoff and landing. The problem arises when the weather deteriorates to near zero visibility and the crew is relying on instrumentation to find that strip of pavement, at 130 knots.

Instrument approaches rely on a narrowing volume of radio signals, the closer one is to the runway. The tighter the signal, therefore, the greater the deviation should something go wrong. Think of threading a string through a funnel, if you touch the edges, you lose. Now do it on a trampoline while someone else jumps on it. I assume we can all agree that wildly porpoising a 200k lb jet, 400 from the ground, chasing a signal, is not a good idea.

Vehicles on the ground are prevented from encroaching on the approach signal area, when aircraft are shooting approaches in reduced visibility conditions, to prevent them for interrupting the signal. In the cockpit you can see your signals fluctuate if someone does cross that threshold. It happens.

When visibility is good, it is a non event but when you can't see jack, having your guidance just start dancing around, gives one moments of pause.

The phones do interfere in some manner. TO what degree, I can't say. I have forgotten to turn my phone off before takeoff and get the annoying beep in the headset when we descend into an area with coverage, so something is going on.

The reason they ask you to turn it off is because they can't tell you its okay, because they haven't tested it. They can't say, well turn it off if it's cloudy or if the bases are below 300'. Some departures and arrivals require precise navigation, even in good weather, for traffic flow reasons. Missing a fix on departure or arrival could cause traffic alerts or aircraft deviations.

All rules exist for the worst possible scenario. Not the milk run. But how do you explain that to the traveling masses? You should be more concerned with the fact those little dixie cup oxygen masks they instruct you to put on in the event of a decompression, won't actually supply you with oxygen when the shit hits the fan at altitude. It's a partial pressure thing.

That's just between you and me...

Edit: At the end of the day, it is the law. If the crew is having a bad day and has a stick up their ass, they can make your day a lot worse. You need to ask yourself, does ignoring the rule, no matter how inane you think it is, really make a body cavity search worth checking the latest XKCD update?

> But how do you explain that to the traveling masses?

I think this has a lot to do with the whole "turn every device off" thing. Keeping aggravation levels down, with tired and stressed passengers, with a large mix of cultures and languages, means that it is much easier to say: everything must be turned off. Otherwise you get into 200 discussions about which devices are allowed, and you have to verify each one.

Each one of these devices is a radio transmitter. Even if it is a receiver, or dvd or HP200lx. They all transmit measurable signals. If two or more are on, this can result in the sum and difference of each pair of signals.

Thus verifying each one is not going to tell the whole story.

Isn't the avionics room under the cockpit shielded to sustain operations through lightning storms, signals bouncing off the ionosphere, solar flares, etc.?

I've flown commercially with my phone left on and privately in Cessnas and I haven't experienced anything negative. My dad's a pilot too by the way and he said that there's no supporting evidence, but this is a just small rule so might as well comply.

There is no supporting evidence. That is part of the problem. The FAA has enough on their hands trying to get the air traffic control system into the latter half of the twentieth century, without trying to test for every stray signal and how it might affect the navigation. A blanket policy, restricting all devices does that.

The wiring is shielded to an extent but there is no special safe room for the avionics. A lot of it is in the nose, right in front of the crew. It is, after all, a very thin tube of aluminum we are all shooting around in. Weight is something to be avoided.

So how do the signals get to the avionics? Let's say that there is an antenna outside the avionics room. It needs to pick up signals. All of these devices emit signals, and some of the signals will go outside the airplane to said antenna.

The plural of anecdote is not data, but stories are fun.

Last Christmas, I was on a multi-hop flight back to SF from the east coast. We were going to be landing in Vegas, and I was talking to a flight attendant. She mentions that conditions in Vegas were a little crazy, as the runway doesn't drain properly and crosswinds are common.

As we're preparing to land, the captain gives the usual speech. It's going to be a little rocky on the landing; there's a sleet storm, etc.

We're making our approach, and the flight attendant gets on the PA. "Someone's cell phone is on. Turn it OFF NOW." A minute later: "Someone's cell phone is still on. I need EVERYONE to doublecheck their phones, and get that phone switched off!"

We ended up diverting to Phoenix, because the pilot did not feel comfortable making an instruments-only landing. His announcement was the only time I've ever heard a pilot sound audibly rattled on the PA.

Did it turn out that anyone actually had his phone on?

How do you imagine they would find that out?

Probably the problem was that during approach pilots had the usual GSM buzz in their headphones while trying to communicate with ATC.

Do you really want your pilots not to hear ATC instructions on take-off, landing or taxi? Like not hearing landing clearance, or which runway exit to use, or what other traffic to lookout for.

Do you even know what was the main cause of the deadliest air disaster (583 dead)? That's right, not hearing ATC instructions.

To be able to hear the gsm buzz in their headphones, the cellphone would have to be on their person, turned on, and be about send/receive some sort of call or data. If a cell phone from a distance away can cause a gsm buzz, then being in an area that has cell phone reception would cause the buzz and they need to design their headphone systems better.

I thought that they did hear the ATC instructions but they were misunderstood.


Same thing happened to me on a Qantas flight out of Adelaide.

Takeoff was crazy turbulent, and the pilot got on the PA several times pleading for "ALL your devices" to be shut off.

Kinda scary. :)

It was the pilot's phone, wasn't it.

If they were really dangerous, I suspect they wouldn't let you have them in the cabin at all. "Everyone turn off your phone" isn't the level of safety compliance major airlines typically rely on.

If they were really dangerous, Al Qaeda would be using them to bring down planes.

That would be like al-Qaeda operatives trying to cause road accidents by not recalling their Toyotas. [Theoretically] increased risk != an effective weapon.

They take bottles of water or cans of coke off you because you might be able to crash a plane with one. They don't take your mobile phone off you, ergo they can't be that dangerous.

Your unspoken premise is that the FAA 1) Cares about safety (more than they care about appearing to care), and 2) That they know what they're doing.

FWIW. I never met someone, who worked for the FAA, who couldn't end my career because they were having a bad day. Pilots feel about FAA officials the way they feel about doctors.

That said, the FAA is the best and safest organization in the world, when it comes to doing what they do. It is bureaucratic, bloated and byzantine and I would take them over any other institution on this side of the Milky Way, any day of the week and twice on Sunday.

Part of the problem is, everyone wants cheap tickets AND the best service. One of my advisors had a sign outside his door. It read: Good. Fast. Cheap. Pick any two.

Good. Fast. Cheap. Pick any two.

That's a big part of it. The other part is the picking. How can I, or the average person, judge the efficacy of safety protocols? I'm sure there are plenty of well-meaning people who invest enormous effort into precautions that are completely invisible to me. But I also know that the cheapest form of employment insurance is being visibly indispensable, which would tend to subsidize highly visible actions regardless of efficacy.

Then you can factor in moral hazard; people take more risks if they feel more safe. This means that if something increases safety, but less than you'd imagine, mandating it can increase danger. e.g. if drivers thought that seatblets made them 99% less likely to die, when the real number was 10%, you'd naturally expect more fatal accidents with more people driving as if their risk of death had dropped by two orders of magnitude.

The beauty of it, as far as the FAA goes, lies in the fact the public is not involved in the safety standards.

There is plenty of window dressing in what the travel industry does. A large part of it is because people want to see something being done. It makes them feel better. No matter how small or inconvenient.

The real safety measures are what we don't see or hear about. Every accident that doesn't happen is not JUST luck. It is the end result of a well thought out and executed process.

Is there room for improvement? Of course. But it beats anything else out there by open lengths.

If you want to be cynical about it, then the FAA also wants to stay out of the public eye any way possible, so it has less paperwork, less scrutiny, and less overhead to deal with.

If you don't feel safe enough flying in US under FAA you can try some more liberal on safety places like Africa or Indonesia. Your survival chances decline can be calculated quite precisely though.

Exactly. There have been several years in the last decade where there were absolutely zero fatalities on US airlines. Say what you want about idiotic security rules, but strict safety measures seem to be working pretty well for us.

I flew a plane for the first time yesterday, it was only a tiny two seater, but with modern electronics. My instructor was using his iPhone during the flight and he didn't seem worried.

Flying a C172 G1000 is not the same as flying a 737-600. You're not shooting RNAV approaches, CAT I ILS, or low alt routes. You shouldn't even be looking at the instruments (I'm sure the CFI has told you).

How about that annoying click/buzz in your headset from the phones TX? It's easy for you to ask your friend/CFI/passenger to turn off their phone but how about a cabin of ~100 people...while flying your approach?

Exactly -- big difference between a 2-seater flying VFR vs. IFR conditions.

Everyone in this sub-thread is right, including you. I've done RNAV and CAT I ILS in a C172(albeit no all-glass cockpit) with no interference from my iPhone(my instructor's phone was also on). I do agree that getting that many people people to turn off their phones(and complying) especially at a critical time would be rather difficult.

My point exactly.

Please, please let's let the airlines keep this rule no matter how little it has to do with safety. If you get an honest answer from a pilot, they'll tell you this was never covered in any flight school, and they usually leave their phone on, but can you imagine a flight where that business guy who just doesn't get it spends the whole time on flight talking on the phone?

Consider this: you're on an eight hours long flight and you need to make a really urgent call. There are no technical reasons why you wouldn't be able to do so, but it is forbidden because some people would abuse it and wouldn't be considerate to other passangers. It's not the phone that should be banned, it's being an inconsiderate prick that should be disallowed.

But until we figure out a way to ban being a prick I'll take the blanket phone ban.

And what is this urgent call about anyway? Maybe to you it seems urgent and to me it just seems like you're being inconsiderate.

Perhaps you are an eminent surgeon and someone is calling you for a life or death consult.

Need to make a short urgent call? Get up, go to the bathroom (which is conveniently sized like a phone booth), make your call, take a piss while you're at it, go back to your seat.

How long before there are signal detectors in the toilets alongside the smoke detectors?

That wasn't my point. I meant if they allowed cell phones on planes, but you didn't want to be a disruptive jerk who talks on the phone on mass transit.

There's a pretty robust wikipedia article about this


Thanks for the link, a few good quotes from there:

Now this I can definately belive: "the report concludes that the primary reason for the ban on cell phone use in flight is that neither the FAA nor the FCC are willing to spend the money to perform conclusive safety tests. "

God flight attendant observations? Thats the evidence that is reliable? How could you isolate for all the other factors? "However a few reports state that anomalies were observed to appear and disappear as the suspect device was turned on and off which would indicate a high degree of correlation."

"Degrees of correlation or confidence were not among the data summarized in the report."

"There is no smoking gun to this story: there is no definitive instance of an air accident known to have been caused by a passenger's use of an electronic device. "

This is my point - are we still in 1984? "will exceed demonstrated susceptibility levels for equipment qualified to standards published prior to July 1984"

BBC report: "most of the evidence is circumstantial and anecdotal. There is no absolute proof mobile phones are hazardous."

"Whether interference from small battery-powered devices should have any influence on electronic systems that should be designed to fly through lightning storms without failing is often disputed by critics of the ban."

To cut the FAA/FCC a bit of slack, its not as easy as one test - one result. There are so many existing permutations of airplane electronics and changing cellphone technologies that its almost impossible and really not economical to test them all. So it is actually much easier to just say no.

This is my point - are we still in 1984?

No, but I'm pretty sure the point is that planes from 1984 are still in use.

Not really.

Planes are removed from service, every internal bit is replaced every few years.

The airframes might be, but they definitely have been upgraded/retrofitted with newer gear.

My favorite is the industrial, hardened switch for 'Internet Off' on Delta flights with onboard Wifi now (which I can't believe I can't find a picture of!).

If I can use WiFi on the plane while it's flying, why not while it's taking off and landing?

Because if something goes wrong the pilots have a lot more of time for a corrective action during flight. Not so much during take off and landing.

"The cost of an accident, should one occur, could be extremely high in terms of human life and the risk is completely avoidable in that no one absolutely needs to use their mobile phone in flight."

compare it to:

"The cost of an accident, should one occur, could be extremely high in terms of human life and the risk is completely avoidable in that no one absolutely needs to eat meat to survive, they can eat vegetables."

I understand what you're getting at here, but eating meat isn't associated with the risk of causing 400 other people to die with you in a fiery plane crash.

Now whether or not such a risk exists is another question entirely.

Unless you like eating the meat of 400 people, anyway.

That's a weak analogy. More like "The cost of an accident, should one occur, could be extremely high in terms of human life and the risk is completely avoidable in that no one absolutely needs to eat meat in flight, they can eat vegetables."

If that was scientifically plausible, I'd be happy to eat my broccoli in flight.

I'd like to know what drove the relatively recent policy shift around demanding that phones and other devices be "completely off" at takeoff and landing, with airplane mode deemed insufficient. From a visual survey of people turning their phones on later, this prohibition seems to be obeyed mostly by one teenager on JetBlue with an iPod once.

I've noticed exactly the opposite on recent flights between NZ and Australia -- they're now a lot more tolerant about having mobiles in flight mode (and specifically say so in the pre-flight announcement) and they let you turn your phone on as soon as the plane has landed. Previously you had to wait until you were "well inside the terminal".

"Well inside the terminal" comes as a surprise -- in the US, the carriers have traditionally tolerated everyone snapping their phones on within a few seconds of touching down. Which is really just another oddity, now that I think about it.

Agree with this, I ussually just hit the lock button my mobile which is in flight mode and this is accepted by the flight attendents

This is strictly anecdotal evidence, but I'll throw in my 2 cents here. I have a private pilot certificate and am working toward an instrument rating right now, which involves being in continuous contact with air traffic control, flying in low / zero visibility conditions, and relying on aircraft instruments to guide me on landings.

On numerous(if not all), I've had my iPhone with me, switched on and even in my lap at times(to use the stopwatch). Occasionally I would keep it in airplane mode on extended flights, but only to conserve battery life. Despite incoming calls and SMSs during these flights, not once have any of the instruments been affected by the phone.

We can all agree that a four-seater Cessna and 767 are very different, but for nav/comm they all use the same instrument systems. I would find it very hard to believe that a larger aircraft wouldn't have more shielding / protection than a simple Cessna with a phone that's just two feet away.

One more thought: Federal Aviation Regulation 121.306 states that no portable electronic devices are allowed except for: portable voice recorders, hearing aids, heart pacemakers, and electric shavers. How are the first and last any different from a phone in airplane mode?

We can all agree that a four-seater Cessna and 767 are very different, but for nav/comm they all use the same instrument systems.

Unlike a Cessna, a 767 has a fly-by-wire system supported by a data bus (e.g. ARINC-429) running the length of the aircraft, often close to the passenger cabin. Presumably, GSM/CDMA signals could interfere with this.

I'll admit that I wasn't aware of this, but on the same token, would that portion of the electronics not be shielded as well?

The 767 was first built in 1981, long before everyone in the passenger cabin was emitting microwave-class RF radiation.

The plane itself serves as a very large shield to outside radiation, but I'm guessing the internal wiring is not RF-shielded because of weight concerns. Wonder how much it costs to rewire a 30 year-old plane.

It cost $368 Million when the FAA forced operators to replace Mylar insulation (cause of at least two accidents):


According to this very interesting IEEE article, it costs anywhere from $1-5M per airplane, which doesn't include lost business cost:


767 doesn't have fly by wire - 777 was the first passenger Boeing to get it. But it does have a lot of wiring.

I've had my cell phone on during a commercial flight before. I had it off on the first leg, turned in on to call my wife during a layover, then forgotten I had done so when they asked me to turn the cell phones off on the second leg because mentally it still was off.

Given the number of flights I have been on (not all that many) and assuming I'm not particularly more or less likely to have this happen than anybody else (I'm feeling comfortably average here), and given the number of cell phones on a flight, I rather suspect that the average commercial flight of a big plane has at least one cell phone on for the duration with probability approaching 1.

Make of that what you will. My point is mostly that the odds that this debate are entirely academic and in fact flights routinely fly with cell phones on are in fact very good.

"Despite incoming calls and SMSs during these flights, not once have any of the instruments been affected by the phone."

Without a fixed reference you have no way to verify this statement. Even if you crossed reference your flight instrument data with a ground-based reference it would not account for intermittent errors that could occur.

Can you clarify what you mean by a fixed reference and a ground-based reference? They sound the same to me, although for the latter I believe you may be talking about a VORTAC or other radio-based ground station, as opposed to pilotage(looking outside and seeing the ground).

Another reason I've heard argued by a coworker is that they aren't banning electronics for the sake of interference, but for your attention.

If anything were to go wrong during a flight, takeoff and landing are the two times that they want you to be able to react with zero hesitation. If something goes wrong and you have seconds to react, the less things you're fiddling with the more likely you are to survive.

This (and other explanations in this thread, like "might fly around") seems to tackle the question from the wrong side, imo.

It seems these reasons are made up by rational minds, trying to understand the ban. Like results from "Why the heck is this prohibited again?" pondering, but completely based on speculation.

So unless we can get some facts to back up these claims, I doubt that these replies help the OP. It sounds more like "Been there, thought about it, this is what I/my coworkers could come up with to explain this mistery"?

That's not a compelling explanation, considering that you're free to keep your head in a John Grisham potboiler (as long as it's not a Kindle edition), or remain fully asleep at takeoff and/or landing.

Well actually I think it's better than jamming the newest (insert band here) album and not be able to hear much other than that and a very dim amount of engine noise.

I think it is safe to say it's likely a combination of many things - this coupled with statistics (as mentioned before, very small % failure rate + very large flight volume = enough dead people to warrant having them turned off) seems the most plausible.

Not to mention that someone linked that it could very well be a problem with the cellular networks - if (hypothetically) you could bugger up an entire major tower with enough "hop" volume, I can see why the FAA or other organization would just want to have this as a cover-our-ass precaution, too.

Former avionics tech here. Not scientific, but I've seen CDMA devices interfere with nav equipment, and GSM devices interfere with communications system (ala the infamous dat-dit-dah GSM sound over speakers). And these on nuke-hardened (EMP-shielded) military systems.

These issues aren't going to crash the plane, however with the sheer variety of cellular devices, it's just a good idea to keep them off.

Besides, you people who can't seem to shut them off are an annoying lot, so there's also a co-passenger sanity aspect to it. Just leave them off, are you that addicted to Farmville?

Not farmville but I enjoy reading on my phone, RSS feeds, kindle books, Instapaper. etc. Short flights espeically in the EU e.g. 1.5 hours to Amsterdam on the weekend in great time to catchup on reading. Missing the takeoff and landing cuts about 30 minutes of reading time.

It sounds selfish and there is enough evidence here that I am now happy to just turn my phone off, maybe I will just print off some of my Instapaper articles :)

I definitely see your point and sympathize (as a busy dad who often gets only 5 minute reading breaks), but even if you aren't gabbing away or noisily typing, most flight environments are dark, and those LCDs leave annoying visual tracers for anyone in your periphery. Can't argue that on a Kindle though :)

There are offline RSS readers, Kindle apps and Instapaper saves can be exported to various formats.

It is all offline, I only read in airplane mode on the phone, I use high contrast mode with medium brightness on the Instapaper app so don't think I really annoy everyone else, but you do get told to turn the phone off even if it is in airplane mode (thus no signal in our out) for takeoff and landing.

I just need to go to super offline mode and print stuff out!

You don't have to turn your phone off during the entire takeoff and landing, just when the stewardesses come to check you.

Apparently that's the only dangerous part.

To expand on my comments, the comm interfence could interrupt voice and data comms transmissions. Although in the latter, it's more like someone picking up the phone while you're dialed into your favorite BBS.

Here is the reason straight from the FAA:

"There are still unknowns about the radio signals that portable electronic devices (PEDs) and cell phones give off. These signals, especially in large quantities and emitted over a long time, may unintentionally affect aircraft communications, navigation, flight control and electronic equipment."


ie. We don't know, but we are playing it safe. While it is an inconvenience, I take comfort in knowing that the regulators are erring on the side of caution when it comes to air safety.

If they are so cautious with the slightest possibility of radio interference from a 3v device, then I can be assured that the remainder of the plane (ie. the thing that is flying at 800km/h at 30k feet with 200+ people inside it) has been checked over and is safe.

How hard could it be to get 500 phones, put them in a plane and dial them all ?

There are more than 500 different kinds of phones.

That's the problem.

Not to mention the different kinds of airplanes, different kinds of electronics, and all possible permutations of the above. Yes, this may seem like overkill to many software devs. Safety-critical systems require huge amounts of testing. It's much more than "release early and iterate."

It's only a problem if the plane doesn't fail.

However, if it fails with those 500 then that's all you need to know to say "phones can down the plane". If you need more detail you can keep researching.

The plane doesn't fail, it's been done. There are too many variables. The biggest problem is older electronics and GSM.

If there's 0.000000001% of anything happen, why risk?

Because you have to live your life? The risk of getting killed in a car accident on the way to work is probably higher than that.

I take plenty of risks greater than 1 in 1,000,000,000.

If you're in the US there's a 1 in 15,000,000 chance you'll die at work today.

The chance of penis fracture during intercourse in any year is about 1 in 100,000,000. I can live with that.

That's exactly what I'm saying. You choose where you take risks, and I'd risk penis fracture every day, but think can postpone a phone call a few hours for the sake of 200 people at 10.000 feet.

Mythbusters did a great show on this problem. Here's a link to the results of the show:


Thanks for that I was really hoping that Mythbusters had tested it. "It was found that cell phone signals, specifically those in the 800-900 MHz range, did intefere with unshielded cockpit instrumentation. Because older aircraft with unshielded wiring can be affected, and because of the possible problems that may arise by having many airborne cell phones "seeing" multiple cell phone towers, the FCC (via enforcement through the FAA) still deems it best to err on the safe side and prohibit the use of cell phones while airborne."

So that is interesting, wonder if they suggested modern shielded planes. Also lends credence to ground interferance as the real reason for the "ban"

But that's the part I don't get; there's no "ban" at all! I can bring a bunch of phones on the plane and just not tell them about it. If they search my bags, they'll remove my 200ml of water citing "it's too dangerous" but they'll leave the cellphones alone.

That's not much of a "ban". So I still disagree that phones could interfere in any meaningful way with any aircraft's systems.

That is a foolish conclusion.

Firstly, if the TSA searches your bags and actually finds a "bunch" of cell phones, I bet that they will find an excuse to hassle you about it.

Secondly, your own example shows how shoddy this reasoning is; the TSA is not rational* about what they confiscate and what they don't -- your water isn't dangerous, and they took it, so why would you trust their judgment on cell phones?

Thirdly, the cell phone industry moves much faster than the airline security industry, so it's (vaguely, remotely) possible that some new phone released yesterday is dangerous, whereas old models aren't; the airlines wouldn't know the difference. One could say the same for almost all consumer electronics. So it would be hard to ban "bad" electronic devices and allow "OK" ones, and probably not worthwhile. Banning them all is an option, but just because it's a risk doesn't mean it's enough of a risk to be worth addressing.

*At least, they aren't rationally trying to prevent planes from being hijacked or interfered with; maybe they are doing a good job at other things, like making people feel warm fuzzies about security.

it's (vaguely, remotely) possible that some new phone released yesterday is dangerous,

That's no greater a possibility than for my netbook, or my wristwatch, for that matter. Why pick on phones over other electronics?

(I suppose the answer is to see your previous paragraph regarding rationality)

They don't pick on phones over other electronics. On every flight I've been on, they ask passengers to shut off "all portable electronic devices," including things that often don't even communicate over a network, like CD players.

Ok, so help me with this. Let's shield the airplane. Now, how useful is your cell phone?

Two things:

1. Using a mobile phone isn't generally dangerous providing everything else on the plane works fine and nothing would be interfered with if it wasn't.

2. Cell handovers at 30,000ft with an air speed around 500mph are really, really hard.

The reasons for turning your phone off during takeoff and landing are wide and varied, but the long and short of it is that it effectively counts as security theatre. Take off and landing are the two most dangerous bits of any flight. If anything goes wrong they do not want people tweeting "OMG IM GOING TO DIE!!!!", they want them focused on bracing for impact. That's not the only reason (or necessarily a major one) but you get the idea.

Since most phones are CDMA now I think the dangers of interference are much much lower. I have always suspected that carriers help promote this myth to reduce network overhead from point 2 above.

I find it hard to believe that a plane's avionics are sufficiently shielded to withstand a direct lightning strike, but one person's phone will crash the plane.

I've heard other explanations, too, such as the fact that too many mobile towers are line-of-sight at the same time, and the effective ground speed means you'd hop towers far too often and it'd mess with the phone system. Multiplied times the number of mobile-phone-carrying passengers in the air at any given time, I suppose it's plausible.

The threat isn't about damaging the plane or forcing it to crash, it is about potential interference with electronic guidance and instruments, especially in the event of an instrument landing.

With a 2 degree glide slope during landing, even a 0.05% change in the radio signal can see a plane hit a mountain as opposed to safely clearing it. Here are two relevant accidents where the instruments were just a fraction off and caused a collision:



That last one is an interesting point, any references to whether it has been tested?


FTA (emphasis added): "Existing rules require cellular phones to be turned off once an aircraft leaves the ground in order to avoid interfering with cellular network systems on the ground."

I find it hard to believe that my tiny MP3 player could be dangerous to the plane's avionics, yet I'm usually told I have to turn it off before takeoff.

That is because they want you to have all your senses (especially hearing so they can give you instructions) during take-off and landing; the most dangerous parts of any flight.

It has nothing to do with the MP3 players themselves.

What about the "radio" stations you can listen to if you plug in to the headrest. I never listen, but do they stop at takeoff and landing? I can't remember if jetBlue turns off your tv during takeoff and landing. I know they turn it off for safetey announcements.

The crew can interrupt that audio at any time with PA or emergency directions.

Nope. Why force people to turn off their kindles but not close their books?

Last time I checked, paperbacks don't have cellular radios.

Neither do some kindles and most other e-readers. Or iPod touches. Or the mp3 player.

They always say, "anything with an on/off switch."

Leave your phone near a CRT screen or loudspeaker, observe the noise right before you recieve a call.

The rest is statistics and probability. What's the probability of interference causing a fatal misreading in aircraft's sensor? Too small. What's the number of flights world wide? Too big. We would see a number of accidents if everyone kept their phones on all the time. As a death is one too many, it warrants the ban.

The "a death is one too many" argument is completely fallacious. If anyone actually believed it, we would all drive our cars at 10 MPH and never fly in planes. Every day we sacrifice human lives for small (or big) conveniences. It's not nice to think about, but it's the way our world works.

1,000 car crashes is not news at all. 1 plane crash or terrorist attack or school shooting is national news and bad PR. Society isn't rational about this. If it was it would disregard school shootings and build more light rail.

Ok how about on airplane mode only so I can still read but not recieve any calls?

Also ban is a bit strong with how it actually works - I mean how do you really enforce that? The air hostesses go around do a quick look but they can miss things, also phones in hand luggage cannot be checked and people can forget it is on, the terrorist scenario I paint above... I mean I design controls for a living and this just does not seem that effective to me if the risk as you say is very low liklihood, very high impact.

Surely a real study needs to be done and if it is really a risk a more effective control like a jammer or electronic tool to detect when a phone is no be put in place.

Or are you arguing that most people turn them off because they get told to and that is enough to mitigate the risk?

Airplane mode is safe but it is problamatic when it comes to enforcing. There's no way for a flight attendant to tell whether idevice is in flight mode.

>Or are you arguing that most people turn them off because they get told to and that is enough to mitigate the risk?

Yes, that's what I meant.

I disagree. The airlines claim the risk of death from my water bottle is too high to allow me to bring the water on the plane. Fine. However, I'm allowed to bring 100 cellphones in a backpack. They don't care about that, except to politely ask me to turn them off.

If there was a remote chance of a cellphone causing a crash - more chance than a bottle with water in it - then they would ban cellphones in flight.

It's very clear that there is no actual risk of interference at all.

Liquids are banned because there were rumours of terrorist plots involving liquid explosives and it was important that something was seen to be done about it.

Carrying 100 mobile phones in a switched on state that have a small probability of interfering with navigation and communication systems would be a ludicrously impractical way of attempting an attack, so airline regulators funnily enough haven't accounted for that possibility.

The water bottle thing is not airlines' doing as far as I know. It's to do with your countries national security authority.

Emirates allows mobile phones on some of their flights.

> The water bottle thing is not airlines' doing as far as I know.

Neither is the cell phone thing in the US. It's both the FAA and FCC:


Go fly in a private plane and leave your cell phone on. I do not fly IFR so I haven't had to rely in my ILS but it does destroy radio communications. Have you ever heard your GSM based phone pulse and cause noise on a close by speaker? Imagine that being pumped into your radios and into your headphones. It is painful to hear. If I was landing when it went off, it could cause me to react badly at a time when I couldn't afford it. Also, I could miss a call that there is traffic around.

Here's the part that I think about: ok I get that phones could potentially cause a problem. If that is the case, than we shouldnt be relying on voluntary compliance. Either it's not a problem--then let people do that they want, or it's a problem, and you better be telling me that you have a better risk mitigation than "hope that everyone turns off their phones".

It has to do with FCC regulations. This is terribly handwavy, because I barely remember the explanation, but basically, they have to make sure that the plane isn't giving off certain signals and interfere with anything, and the easiest way to do that is just to tell everyone to switch their devices off.

Hopefully someone can clarify that a bit.

> they have to make sure

This is the problem, though. They don't make sure! They politely ask you to turn your phone off. 50% of people comply, 50% don't. If they actually had to stop the signals, they would ban all cellphones in the cabin. They could collect them, put them in a lead case with the luggage and move on.

But since they don't "make sure" of anything, I disagree with your explanation.

Do the cellphones even work in airplanes? I mean, they are pretty far from antennas, even over civilized area. They also move quite fast, although I do not really know how much Doppler effect affects the phones' transmitters and receivers. The plane is also a Faraday cage, thus it may greatly reduce signal.

GSM is designed to be usable when travelling in a car, but going much faster than that will likely cause problems. It's probably problematic that you're not staying long enough in a single cell tower's range, and doppler effects on the radio signals will also cause problems (if I remember correctly from my uni course on the subject).

From experience I can tall that cell phones seem to work up to an altitude of about 7000ft in slow-flying aircraft (ask a skydiver).

Not well, but they can work (9/11 proved this pretty conclusively). It depends on where, how fast and how high up you are.

As far as I'm concerned, reason #1 to ban cell phones on airplanes,

Who wants to listen to the person beside you talk through the flight on a cell phone. Your life can be on pause while you fly through the air.

I've heard it summarized thusly:

The aircraft is most likely to hit something during takeoff and landing. Cell phones, laptops, and other hard, dense, chunks of metal plastic are, in fact, dangerous when they're flying toward your head.

It doesn't particularly matter whether they pose an electronic threat, policy would be the same.

Wouldn't that just mean the policy should be put them away not turn them off?

I was thinking of this 2 days ago, when I decided to leave Runkeeper running in my pocket :)

I don't want to encourage terrorism, but if someone wanted to destroy an airplane, they could bring onboard a more dangerous device disguised as a phone or other everyday 'black box' object such as a laptop. The dangerous device might emit serious levels of radiation, it might contain a powerful laser, it might contain explosives. The best defense against 'terrorism' is to be nice to other countries, help them and don't oppress them.

Usury (national debt), bombing, invasion and economic sanctions (aka starvation) are not nice. The countries and groups that commit crimes like those are likely to be attacked. Don't be bad, and no one will want to kill you.

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