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I do think the complacency issue might be a component here. Humans tend to quickly accept recent history as "normal" and over time forget the lessons learned by past disasters.

"Those who don't remember history are doomed to repeat it"

It's been a couple of decades I think, maybe more, since an engineering screwup affected a passenger airliner like this. You could argue that the 787 LiIon battery thermal runaway thing was a red flag. That also resulted in an FAA grounding, but that was fairly easily remedied and nobody died.

Read the narrative in the report. Why do you suppose that after they got the same initial signs of trouble that the Lion Air flight had (stick shaker on left side, disagreement in airspeed values, etc. immediately after takeoff) that the captain tried to engage autopilot and instructed the first officer to retract flaps and inform controllers they were proceeding to climb to FL 320 (32,000 ft). Why not instead turn back and land and hand the aircraft over to maintenance?

From the report:

At 05:38:44, shortly after liftoff, the left and right recorded AOA values deviated. Left AOA decreased to 11.1° then increased to 35.7° while value of right AOA indicated 14.94°. Then after, the left AOA value reached 74.5° in ¾ seconds while the right AOA reached a maximum value of 15.3°. At this time, the left stick shaker activated and remained active until near the end of the recording. Also, the airspeed, altitude and flight director pitch bar values from the left side noted deviating from the corresponding right side values. The left side values were lower than the right side values until near the end of the recording.


At 05:39:06, the Captain advised the First-Officer to contact radar and First Officer reported SHALA 2A departure crossing 8400 ft and climbing FL 320.


At 05:39:42, Level Change mode was engaged. The selected altitude was 32000 ft. Shortly after the mode change, the selected airspeed was set to 238 kt.

At 05:39:45, Captain requested flaps up and First-Officer acknowledged. One second later, flap handle moved from 5 to 0 degrees and flaps retraction began.

Bear in mind stick shaker and divergent instrument readings all this time.

Why not just return and land, leave the flaps configuration alone (which would have inhibited MCAS), especially since this is exactly how the Lion Air flight started.

I know this is easy to critique from the comfort of my chair, and the pilots are not here to defend themselves, but some things in this narrative just don't make sense.

With hindsight, we know that retracting the flaps was a bad idea.

But check Boeing's MCAS bulletin, which is the only official information pilots received about MCAS at the time of the flight.


It makes zero mention of flaps. It doesn't recommend avoiding retracting them or trying to land as soon as possible.

Trying to land as fast as possible is typicality a bad idea. Planes which have just taken off are almost always over their maximum landing weight. Even if you ignore that, the extra stress of trying to land as soon as possible could cause the pilots to make more errors.

Procedures for issues on take off are typically focused on continuing to climb to gain as much altitude as possible to give the pilots time and space to assess the problem before dumping fuel and landing. The more altitude you have the more time you have to recover.

And unfortunately, climbing through 5000 feet requires retracting the flaps.

Check the airspeed at the time they raised flaps. It was right at Vfe, and increasing.

I don't know the most likely consequence of flying with flaps 5 above Vfe. Maybe flaps would (asynchronously) depart the airplane, or induce flutter at a much lower than usual airspeed. Either of those is an extremely high risk of losing the aircraft.

Stick shaker activation isn't a rare event. Quite a lot of stick shaker events happen in low risk situations. And quite a lot of them are false positives. http://www.atsb.gov.au/publications/2012/ar-2012-172.aspx

Experience sounds like a good thing on the face of it, but it also adds noise where all of these indications sound familiar enough, and yet nothing in particular stands out and tells you to leave flaps alone. That suggestion isn't even in the emergency airworthiness directive. And still at the time of this event there's no simulator that can be configured for MCAS upset so that pilots can experience it in various phases of flight.

Also, the priority in a flight control problem is to fly the plane, get it stabilized, understand the problem, and turning back to the airport is inconsistent with that. Fly runway heading is the proper thing to do, it's less complicated. A turn increases angle of attack, increases drag, it makes a high angle of attack situation worse, and if you're trying to climb it reduces your rate of climb.

Of course they would have tried to land after getting the plane under control. They didn't have airspeed or altitude under control, and were following the checklists they were supposed to be following. IAS Unstable tells them to leave thrust high and flaps alone to avoid a wing stall.

The pilots didn't actually do that. They did not use electric stabilizer trim to "neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT" in fact the trim had been run markedly down by MCAS by the time they switched off the electric trim.

Classic illustration of why conversations between geeky technology people and "normal" people usually and in awkward silence after about two minutes.

I have totally given up on even trying to explain what I do at work. It never leads to anything.

At the same time, I used to do speed dating and too often had to hear the poor guy next to me confuse "what do you do?" with "what exactly do you do day to day in as painstakingly technical detail as possible?" when the other party doesn't even know if they're an astronaut vs full-time dog walker.

I see this playing out in a couple of possible ways. One is that it ends up like the DC-10. Public confidence is lost, even though the problem is fixed. The aircraft end up going into freighter service.

The other is that they make a convincing case that the problem is resolved. I don't know if that's possible given today's default hate for big corporations, we'll see. They've done it before with the 737 and the rudder problem it had in the 1990s or so. That problem led to a few fatal crashes, but I'm not sure it ever got the attention that this story is getting. The news cycle was different then.

I would absolutely fly on one once the problem is corrected.

Be my guest. For sure I won’t be aboard one of these death traps in the next accident. And we’ll have another accident if they let this killing machine take off again given that they are just doing a useless software fix.

In all fairness this plane is only a danger to its crew (and to regular commuters). Even without the software fix, the probability that you get into a crash in one of the few times in a year when you make a leg in this plane is still infinitesimal. For the crew that spends the whole year in there, different story.

By my calculation the plane was flying roundabout 100.000 days with 2 accidents. Assuming 2 round-trips a day maybe 200.000 takeoff during this time. One crash every 100.000 take-offs.

Now assuming 40.000 road deaths per year in the US and 300.000.000 citizens we have 0.000133 probability to suffer a road death a year. Assuming one 737MAX round trip per quarter we have 8 take-offs so .00008 probability to die in a 737MAX. Assuming commuter 40 trips a year we have a risk much higher than the average road death risk.

I assume that AoA sensor disagree would have been warned about still on the ground. Even if both fail, a new take off checklist will probably include comparing AoA information with analog instruments. If one sensor failure is 10E-5, two simultaneous should be 10E-10, multiplied with assumption of competence (say 99/100 will now know how to deal with it), which gives 10E-11 - 10E-12. I.e. I wouldn't worry about MCAS anymore after every plane has been updated.

What I would worry about is departure stalls, as MCAS doesn't seem to solve these. I wonder whether there isn't another 10E-5 to 10E-6 risk in there and people have just been lucky so far. Another MAX8 crash involving a stall would kill this plane I think, as it would prove much more that it's inherently unsafe.

> If one sensor failure is 10E-5, two simultaneous should be 10E-10.

That only holds if errors are statistically independent. See also Common Mode Failure [1].

[1] https://en.wikipedia.org/wiki/Common_cause_and_special_cause...

From the FDR data in the report, it seems that the AoA sensor disagreements on this flight didn't start until after takeoff. I don't know if this is the normal failure mode.

Indeed. The speculation is that it was caused by a bird strike during takeoff.

That is not how plane safety is done.

> I would absolutely fly on one once the problem is corrected.

The problem is Boeing, not the MCAS system.

I don't think Boeing can be fixed.

At the very least it seems that some specific "differences training" on MCAS should have been included. I don't know at what point the differences are enough to require a new type designation.

Yes, pilots selecting "up" on the trim switch should stop and override MCAS. But it also "resets" MCAS so that it will pitch down again on its next cycle. So you'd have to be constantly correcting it, or switch the electric trim off entirely (i.e. treat it as runaway trim).

Or toggle the trim control switch when MCAS starts up again.

Post Lion Air, they should have known that.

Why exactly? if Boeing did not updated the manuals and checklists how would pilots know that? from internet forums? Should a pilots ignore the checklists and try steps he read on the internet ?

I could not find if Boeing updated their manuals/checklists after the first crash.

Yes, Boeing issued this service bulletin after Lion Air:


And the FAA made it an emergency airworthiness directive in response.

The steps on it were broadly followed by the Ethiopian flight.

Am I missing it because I don't see flaps mentioned anywhere in that link.

You're not missing it. The pilots followed the instructions, and the instructions do not mention flaps.

This bulletin notes that electric stabilizer can be used to neutralize the control column prior to STAB CUTOUT, which it appears the Ethiopian crew did not do.

They did so repeatedly.

The bulletin completely fails to note that if you don't time the STAB CUTOUT immediately after you use manual electronic control but instead the MCAS acts again before you cutout, you're left trying to manually trim the stabilizers in a situation where the elevators are putting so much force on the jackscrew that manual stabilizer trim may be impossible.

That's what got this flight.

Appears? Where are you reading this to come to that conclusion?

Page 11 of the preliminary report, 05:40:35 "stab trim cut-out".

Page 26, five manual trim up inputs before that time. Manual trim is electric trim instigated with yoke toggle switch.

What is not certain (to me) is if continuous nose up toggle for sure would have inhibited the automatic nose down from MCAS shown at 05:40:45. It really looks like pitch trim still needed to come up more in order to relieve the control column force to bring it back to neutral.

Why didn't they continue to manually trim (electric) after 05:40:35 to relieve yoke back pressure and also to improve climb rate and also reduce speed? I suspect they actually got ahead of themselves, setting trim stab cutoff too soon, not realizing how much more insideous the MCAS upset case is compared to runaway stabilizer trim.

And that is the problem with no training. They had no way to iterate various scenarios of working and failed MCAS behaviors.

It seems the "yo-yo manoeuvre" required to manually trim when severely mistrimmed with deflected elevator stopped being taught or mentioned in Boeing manuals decades ago.

Pilots should have known that MCAS is inactive with flaps extended, per information from Boeing.


The Boeing/FAA directive re: MCAS does not instruct them to extend flaps.

Further, there's other things going on in the cockpit due to the malfunctioning AoA sensor that's the root of all this.

Specifically one of the effects is that they get an Unreliable Airspeed Indication, and run that checklist. That checklists memory items include maintaining the current flap configuration (in this case, flaps up).

The Boeing/FAA directive does not instruct them to deviate from this and extend flaps. They have a checklist memory item instructing them to in fact do the exact opposite, and not touch flaps.

You're correct that the AD and runaway trim procedure does not instruct them to extend flaps. What I was addressing was the statement upthread that "Flaps out supposedly would have kept MCAS off but the pilots weren't expected to know that."

If I'm a 737 MAX pilot, after the Lion Air crash I'm learning absolutely everything I can about MCAS. And from information Boeing provided I would learn that it operates with autopilot off, flaps up, at high indicated AoA.

You mention unreliable airspeed, that was actually their first problem. Flaps were extended at that point, as according to the narrative they were not retracted until after the AoA disagree, stick shaker, and airspeed disagree. In fact it almost reads like they were intending to continue the flight, engage autopilot, and climb to 32,000 ft with the stick shaker going the whole time. That seems very odd to me.

>If I'm a 737 MAX pilot, after the Lion Air crash I'm learning absolutely everything I can about MCAS. And from information Boeing provided I would learn that it operates with autopilot off, flaps up, at high indicated AoA.

And in a crisis situation you skip the checklists and think fast and apply your instincts because you read something on a forum? Sure if you have a lot of time you can try thinking but this is not debugging a bug where you have hours to observe the issue, try different inputs, observe again, Google some questions etc..

We don't want pilots to be creative. Air safety is so good because pilots learn memory items and checklists and actually follow them instead of making stuff up.

If the checklist doesn't mention flaps and the plane crashes if you keep the flaps up, that's on Boeing.

Interesting, that when they turned the electric trim back on, they only momentarily blipped the switches to trim up, and the stabilizer did move. Then five seconds later MCAS pitched down again and it was over.

Wonder why didn't they trim up more when they turned the electric trim back on. On the surface it appears that was their last chance to salvage the situation.

That's what I think is most interesting. Given the position they found themselves in, going against the directive from Boeing to leave the trim cutout for the duration of the flight, means they were desperate to get the trim back up. So why did they not immediately make use of the reenabled electric trim control to counteract MCAS for as long as it took? They had kept the plane flying up until reenabling the electric trim, but that one action pushed it over the edge and could not be reversed? Confusing.

They made two small trim up commands. But looking at the flight data graph, the stablizer on the bearly moves. The motor was probably stugling against the aerodynamic forces too.

Prehaps they didn't think it moved at all and decided they stablizer was jammed. 5 seconds later, MCAS commands down and because that's in the same direction as the aerodynamic forces it moved a lot easier.

They are also pulling with all their might on the yoke and have been for several minutes. At this point probably fighting fatigue or even getting close to muscle failure (how many pounds of force for how long?) and starting to question their sanity.

Yeah, from my computer screen I can wonder why they didn’t sit on that ANU switch hard and long. But in that cockpit Boeing had already sealed their fate.

tl; dr: the false positive rate is too high.

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