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

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

#181

Post by mhandley » Thu, Apr 04, 2019, 1:04 PM UTC

alkonaut wrote: post #145

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…

I'm an armchair non-expert at best: but shouldn't planes always be controllable by the column so long as the plane is mechanically OK? I.e. max power + pull stick should always just take the plane up, regardless of any amount of misconfiguration such as being out-of-trim etc? Isn't that a reasonable expectation? That is: a pilot in panic at low altitude should never be required to do anything more than he basically c…

Trim is much more important in a large jet than it is in a Cessna because of the speed range it operates over. At lower speeds with flaps up, you need a high angle of attack to maintain altitude. This entails a very high stick load in a manual aircraft like a 737 unless you trim nose-up for it. With flaps down, you need much less angle of attack, so less nose-up trim. At higher speeds, flaps up, you need a low angle of attack, so trimmed much further down. At higher speeds still, you start to get mach tuck, and need to trim up a little. So that's quite a large range of angle of attack, and so trimming needs to be very effective.

Now, at the same time, the airframe is not rated for aerobatics. So, you don't want to fit a huge elevator, because then it would be too easy to pull high-G maneouvers, and damage the airframe. It's all a compromise - very effective trim is a necessity in a large jet, and the elevator should be just large enough to give the control needed. The limitation then is that there may be parts of the flight envelope where the aircraft can be so far out of trim that the elevator struggles to overcome the trim. Normally well trained pilots would go nowhere near these parts of the flight envelope. This is why it's really not helpful when the automatics go awry, and put you there.

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

#182

Post by rutthenut » Thu, Apr 04, 2019, 1:05 PM UTC

Some other info aggregated here https://www.theverge.com/2019/4/4/18294317/boeing-737-max-et...

Clear to most that the software has/had an appalling design for error-handling, with tragic results, and blame from Boeing to deflect that

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

#183

Post by treis » Thu, Apr 04, 2019, 1:05 PM UTC

CaptainZapp wrote: post #176

treis wrote: post #165

Earlier quoted context omitted.

>the Lion Air crash (they were busy smearing the airline an the pilots instead) In a rush to put to blame on Boeing everyone seems to have forgotten that Lion Air badly screwed up: (1) The aircraft exhibited the same failure on its previous flight. Not fixing it before the next flight is a huge maintenance screw up. (2) That failure and the steps to correct it should have been in the log book and the next pilots shou…

I think it's pretty disgusting that you're still smearing the Lion Air Pilots despite all the facts that came to light after the Ethiopian crash. Namely that Boeing didn't even bother to document MCAS, let alone deem it necessary to provide training for purely commercial reasons. Turns out that their documented emergency procedure also isn't helpful once the plane becomes unstable due to their design fuck-up. Way to…

>I think it's pretty disgusting that you're still smearing the Lion Air Pilots despite all the facts that came to light after the Ethiopian crash.

Thank you for your personal attack.

Besides that, I'll just note that you didn't actually address any of my points.

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

#184

Post by JshWright » Thu, Apr 04, 2019, 1:08 PM UTC

treis wrote: post #165

CaptainZapp wrote: post #122

Earlier quoted context omitted.

Totally agree. Some of the sentiments expressed here was borderline racist. (badly trained, overworked cluelless third world pilots not even capable to follow a checklist). One of the worst smear jobs was actually by the New York Times accusing the captain of the Ethiopian plane not having trained in a 787-MAX simulator. Hello? Wasn't that the whole sales pitch that the plane requires no training at all for certified…

>the Lion Air crash (they were busy smearing the airline an the pilots instead) In a rush to put to blame on Boeing everyone seems to have forgotten that Lion Air badly screwed up: (1) The aircraft exhibited the same failure on its previous flight. Not fixing it before the next flight is a huge maintenance screw up. (2) That failure and the steps to correct it should have been in the log book and the next pilots shou…

As we have now learned, switching to the manual control is useless when the aircraft is in this condition (high speed, stab down, elevator up).

The Ethiopian pilots turned off the electric trim control, only to have to turn it back on again.

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

#185

Post by peteradio » Thu, Apr 04, 2019, 1:12 PM UTC

matt4077 wrote: post #170

peteradio wrote: post #154

Earlier quoted context omitted.

Why is nobody looking at the manufacturer of the sensor?

For reasons similar to those often cited not to blame a single operator when they accidentally drop the production database. It seems these sensors, and also pitot tubes, are notoriously unreliable. That is likely to be function of them being mechanical (moving parts) systems in rather unaccomodating environments, I. e. freezing cold, strong winds, etc. In such a scenario, one has to acknowledge the shortcomings, ins…

Makes sense, I guess I wonder what the stated demands were of these sensors and whether they were built to reliably meet that demand.

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

#186

Post by JshWright » Thu, Apr 04, 2019, 1:12 PM UTC

sokoloff wrote: post #129

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 am one of those people. If in fact the stab trim cutout switches were set to cutout early in the incident sequence, as required by the memory items on the checklist, I will absolutely retract my criticism of the crew and the blame falls much more squarely/exclusively on Boeing. I’ll make it a point to retract and apologize on all three forums where I made those comments (two tech and one aviation). I don’t read the…

Shouldn't that be the other way around?

You're the one making the claim that the pilots acted inappropriately. Now you're saying you require evidence contradicting your claim before you retract it?

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

#187

Post by drunken-serval » Thu, Apr 04, 2019, 1:16 PM UTC

Shank wrote: post #160

alkonaut wrote: post #145

Earlier quoted context omitted.

I'm an armchair non-expert at best: but shouldn't planes always be controllable by the column so long as the plane is mechanically OK? I.e. max power + pull stick should always just take the plane up, regardless of any amount of misconfiguration such as being out-of-trim etc? Isn't that a reasonable expectation? That is: a pilot in panic at low altitude should never be required to do anything more than he basically c…

> but shouldn't planes always be controllable by the column so long as the plane is mechanically OK? The problem is that you can easily exceed the aircraft flight specifications if you enable unlimited control. If you pull the stick back at max power you can seriously risk the creation of a stall, which is why MCAS exists in the first place. The whole goal Boeing had was to create a safe plane by letting software ens…

> You would hope this, but what makes the determination that the pilot is at a low altitude

Radar altimeter. Any aircraft with autoland capability should have three of them.

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

#188

Post by usrusr » Thu, Apr 04, 2019, 1:17 PM UTC

rocqua wrote: post #4

If this was indeed MCAS, it is my understanding they 'could have' stopped this by turning off power to the electronic stabilizer trim.

But when the electric trim is completely shut down, manually restoring a sane trim position takes a very long time and time can be limited while close to the ground.

I think that what they would have needed was an intermediate mode, "disable the decisionmaking, but keep the power-assist". But that would only make the checklists even more complicated, at the cost of valuable time and more possibilities for user error.

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

#189

Post by saiya-jin » Thu, Apr 04, 2019, 1:18 PM UTC

skrebbel wrote: post #91

jakecopp wrote: post #58

Earlier quoted context omitted.

Hard engineering problem - where do you open up the fuselage to get the people out? It's a tube so you can't weaken it. You also can't open a hole at the back and let them slide out backwards, you'd need a cylindrical tube in a tube which can then slide out. That's a HUGE amount of extra weight and complexity. Planes are so so much safer than cars. Before we parachute people out of passenger planes we should be eject…

> Before we parachute people out of passenger planes we should be ejecting people out of the roofs of cars if an imminent collision is detected :) I'd be "accidentally" driving into a lot of trees if cars had that. Sounds like major fun!

Not really, fighter pilots can do 2 or 3 of those and then have to retire due to compressive damage on their spines. The Gs involved are not benign, since it needs to also cover the case of pilot ejecting on land quickly.

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

#190

Post by treis » Thu, Apr 04, 2019, 1:18 PM UTC

JshWright wrote: post #184

treis wrote: post #165

Earlier quoted context omitted.

>the Lion Air crash (they were busy smearing the airline an the pilots instead) In a rush to put to blame on Boeing everyone seems to have forgotten that Lion Air badly screwed up: (1) The aircraft exhibited the same failure on its previous flight. Not fixing it before the next flight is a huge maintenance screw up. (2) That failure and the steps to correct it should have been in the log book and the next pilots shou…

As we have now learned, switching to the manual control is useless when the aircraft is in this condition (high speed, stab down, elevator up). The Ethiopian pilots turned off the electric trim control, only to have to turn it back on again.

>As we have now learned, switching to the manual control is useless when the aircraft is in this condition (high speed, stab down, elevator up).

That wasn't the position the Lion Air flight was in.

I don't think there is much debate that the Lion Air flight was recoverable since the pilots on the previous flight recovered from the same issue:

>As the Lion Air crew fought to control their diving Boeing Co. 737 Max 8, they got help from an unexpected source: an off-duty pilot who happened to be riding in the cockpit.

>That extra pilot, who was seated in the cockpit jumpseat, correctly diagnosed the problem and told the crew how to disable a malfunctioning flight-control system and save the plane, according to two people familiar with Indonesia’s investigation.

>The next day, under command of a different crew facing what investigators said was an identical malfunction, the jetliner crashed into the Java Sea killing all 189 aboard.

https://www.bloomberg.com/news/articles/2019-03-19/how-an-ex...