Ethiopian Airlines Boeing 737 pilots 'could not stop nosedive' • Hacker News Board

Re: Ethiopian Airlines Boeing 737 pilots 'could not stop nosedive'

#101

Post by qaq » Thu, Apr 04, 2019, 11:21 AM UTC

mhandley wrote: post #99

qaq wrote: post #97

Earlier quoted context omitted.

Why speculate here's memory item (pilot should know without looking at the manual) for all 737s for runaway stabilizer. Do you have any information they followed this. All published information we had was specifically that they did not follow the procedure: CONTROL COLUMN - HOLD FIRMLY AUTOPILOT (if engaged) - DISENGAGE Do not re-engage the autopilot. Control airplane pitch attitude manually with control column and m…

From today's Ethiopian Airlines press release: "The preliminary report clearly showed that the Ethiopian Airlines Pilots who were commanding FlightET 302/10 March have followed the Boeing recommended and FAA approved emergency procedures to handle the most difficult emergency situation created on the airplane. Despite their hard work and full compliance with the emergency procedures, it was very unfortunate that they…

Thats a press release there is cockpit audio pilots vocalize actions when they take them the cutout switches were never turned off. Would you point to the part of the actual report that says the position of cutout switches was off?

Re: Ethiopian Airlines Boeing 737 pilots 'could not stop nosedive'

#102

Post by marsRoverDev » Thu, Apr 04, 2019, 11:26 AM UTC

vfinn wrote: post #46

Every time I read about these plane accidents, I wonder why planes don't have any emergency features to save these people. Couldn't you build a plane that would eject the cabin as a parachute module or something. Yes, I'm sure this is naive, but why? Edit: My point is that almost anything is better than crashing down with the plane.

Because said system would be very heavy, and probably on balance it would result in more crashes due to an increased number of failure modes.

Re: Ethiopian Airlines Boeing 737 pilots 'could not stop nosedive'

#103

Post by TheOtherHobbes » Thu, Apr 04, 2019, 11:26 AM UTC

fulafel wrote: post #82

TheSpiceIsLife wrote: post #75

Earlier quoted context omitted.

The question then becomes are can a plane fly with each of those attached by structural bulkheads & explosive bolts. The remaining ‘crew and passenger capsule’ would need to remain sealed.

Maybe solid forms could be explosively or electrically welded off.

No.

This speculation is just pointless. It's simply not a solution given the engineering practicalities and cost constraints.

It's also not a good way to solve what is essentially a software problem.

Well-designed planes are ridiculously safe compared to almost any other mode of transport. And it's completely possible to design planes that handle all but the most extreme and unlikely edge cases.

The problem here isn't that passengers didn't have a Rube-Goldberg escape route, but that Boeing made some serious design errors - and then apparently tried to cover them up.

Re: Ethiopian Airlines Boeing 737 pilots 'could not stop nosedive'

#104

Post by mhandley » Thu, Apr 04, 2019, 11:28 AM UTC

qaq wrote: post #101

mhandley wrote: post #99

Earlier quoted context omitted.

From today's Ethiopian Airlines press release: "The preliminary report clearly showed that the Ethiopian Airlines Pilots who were commanding FlightET 302/10 March have followed the Boeing recommended and FAA approved emergency procedures to handle the most difficult emergency situation created on the airplane. Despite their hard work and full compliance with the emergency procedures, it was very unfortunate that they…

Thats a press release there is cockpit audio pilots vocalize actions when they take them the cutout switches were never turned off. Would you point to the part of the actual report that says the position of cutout switches was off?

The preliminary report is not yet public - Ethiopian have seen it, hence their press release, and some of the media have been briefed on its contents, hence the BBC article, but it's not yet public.

Re: Ethiopian Airlines Boeing 737 pilots 'could not stop nosedive'

#105

Post by losvedir » Thu, Apr 04, 2019, 11:33 AM UTC

matt4077 wrote: post #12

I’d love to see those people who accused the airline and crew of being incompetent to apologize in the light of these reports. It was shameful to see Boeing actively encouraging that narrative behind the scenes. Especially considering it plays on racist stereotypes equating „Africa“ with bad training/bad safety record/…. The idea of „dingy third world airline“ was ridiculous on its face, considering how bad a fit fly…

I've never seen anyone blame the crew, as it was recognized from the start that this was probably MCAS. I've seen, and personally believe, that a more experienced crew could have saved the flight, but that's different from calling this crew incompetent.

I wish the article was clearer on what procedures were followed that didn't work. Did the crew follow the runaway stab trim checklist? If so, then that's really bad for Boeing, but I can't find anything specific yet.

Re: Ethiopian Airlines Boeing 737 pilots 'could not stop nosedive'

#106

Post by golergka » Thu, Apr 04, 2019, 11:35 AM UTC

FactolSarin wrote: post #45

golergka wrote: post #38

Earlier quoted context omitted.

> It was shameful to see Boeing actively encouraging that narrative behind the scenes. Is it shameful because we suspect that it was an intentional lie on their behalf, or is it shameful even if it was honest opinion of these Boeing representatives at the time?

Either. Deeply seated racist beliefs are often honestly held, but that doesn't make them less shameful.

Why do you think that racism would be the only reason to hold such a belief in this particular situation?

Re: Ethiopian Airlines Boeing 737 pilots 'could not stop nosedive'

#107

Post by VBprogrammer » Thu, Apr 04, 2019, 11:35 AM UTC

mhandley wrote: post #89

TheSpiceIsLife wrote: post #70

Earlier quoted context omitted.

Is anybody here capable of calculating the force required to move the trim tabs on a 737MAX at 310 knots at low altitude? I imagine at that speed there would be quite some force on the elevator and trim tabs.

There's no trim tab on a 737 - the whole horizontal stabilizer is moved to trim the aircraft in pitch. Normally this is done electrically, but the stabilizer jackscrew can also be moved using manual trimwheels that move the jackscrew using physical cables. Whether this is possible at high airspeed while the stabilizer is trimmed nose down, and the elevator is being pulled up as hard as you can to avoid diving - that'…

Something else I've started to wonder about is what the manouvering speed is on a 737.

I can't find a good reference but 280 knots is suggested as a turbulent air penetration speed which should be in the same ballpark

Applying full back elevator above this speed can bend the airplane (cyclic movements even more so).

Re: Ethiopian Airlines Boeing 737 pilots 'could not stop nosedive'

#108

Post by crocal » Thu, Apr 04, 2019, 11:41 AM UTC

prmph wrote: post #61

Maybe this is a naive question, but why can't the automated controls on plane be designed such that: 1. They can be independently disabled? 2. For MCAS in particular, disabling it will automatically revert to the previous trim level before it shuts off? 3. They can rely on sensors that are kept in enclosed storage (thus much less likely to fail due to freezing, etc) and immediately deployed when there is a problem wi…

Implementor of similar systems here.

1. It's possible, but you have to understand that a pilot, however bright he may be, cannot be overloaded with too many modes of operations. You can't always have Neil Armstrong driving...

2. We have to wait for the conclusions of the investigation. There is obviously still a lot of question marks about what /should/ occur and what /did/ occur, so it's difficult to speculate (at least for me) on what a correct implementation of the system should have been.

3. Each sensor has pros and cons. For an AOA, I am not an expert, but well, it's supposed to measure the lift under the wing, so I don't see how you can avoid being outdoor to get a direct measure of this quantity. I believe someone on HN more expert could give more insight here, but my experience when you try to use indirect sensors is that it générâtes the need for /more/ computational complexity to deduce the intended measure from indirect sources.

For your last comment, I would complement that auto pilots malfunction due to sensors going bad /unnoticed/.

We should take "going bad" very broadly: either the sensor is broken, or it is not picking up something that it should because, well, the designer just did not think about it.

Re: Ethiopian Airlines Boeing 737 pilots 'could not stop nosedive'

#109

Post by dsfyu404ed » Thu, Apr 04, 2019, 11:42 AM UTC

dagaci wrote: post #86

matt4077 wrote: post #12

I’d love to see those people who accused the airline and crew of being incompetent to apologize in the light of these reports. It was shameful to see Boeing actively encouraging that narrative behind the scenes. Especially considering it plays on racist stereotypes equating „Africa“ with bad training/bad safety record/…. The idea of „dingy third world airline“ was ridiculous on its face, considering how bad a fit fly…

It actually seems to be normal practice to quickly allocate blame, even when its quite clear that little if any investigation has actually taken place. One of the effects of allocating blame is that large swathes of the general public will "switch off" and not ask questions of their politicians, who in turn apply little pressure to improve or advocate for improved standards (which big business and comfortable institu…

>It actually seems to be normal practice to quickly allocate blame, even when its quite clear that little if any investigation has actually taken place.

Readers would do well to remember this also applies to all the people who were 100% sure it was MCAS related before the wreckage even stopped smoldering.

Re: Ethiopian Airlines Boeing 737 pilots 'could not stop nosedive'

#110

Post by dingaling » Thu, Apr 04, 2019, 11:43 AM UTC

mhandley wrote: post #7

Will be interesting to see the details when the report is actually public. It does sound like the scenario that Mentourpilot explored in the simulator is close to what happened, namely: Bad AoA probe causes MCAS to trim down, and also to indicate IAS disagree. Pilots increase throttle as per non-normal checklist to reduce the risk of stalling due to unreliable airspeed. Pilots disable electric stabilizer trim, as per…

A bad AoA probe wouldn't trigger IAS disagreement alert ( that is fed from the separate pitot tubes ) but could activate the corresponding stick-shaker which may make the pilots consider the possibility of IAS uncertainty.

Just a minor quibble.

Also increasing airspeed isn't a panacea for avoiding a stall, it is entirely possible to enter a high-speed stall if the AoA isn't managed. And in fact as mentioned speed can make recovery more difficult due to airloads on non-FBW aircaft.