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Ethiopian Airlines 737 MAX Investigation Preliminary Report

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Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#221

Post by VBprogrammer »

na85 wrote: post #202
VBprogrammer wrote: post #187

Earlier quoted context omitted.

If my reading of the graphs is correct they are above Vmo for most of the episode. I'm surprised the flight surfaces weren't torn from their hinges.

Vmo incorporates a factor of safety in its specification, so exceeding it is not a "parts fall off the aircraft" event. Vne is where things start to get scary because it's usually based on flutter, which can catastrophically damage/destroy the aircraft in very short order.

Yes. But it doesn't include full control deflections and certainly not control deflections in opposition to one another. Even at Va rapid control movements and control movements in multiple axes can permently damage the aircraft.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#222

Post by na85 »

VBprogrammer wrote: post #221
na85 wrote: post #202

Earlier quoted context omitted.

Vmo incorporates a factor of safety in its specification, so exceeding it is not a "parts fall off the aircraft" event. Vne is where things start to get scary because it's usually based on flutter, which can catastrophically damage/destroy the aircraft in very short order.

Yes. But it doesn't include full control deflections and certainly not control deflections in opposition to one another. Even at Va rapid control movements and control movements in multiple axes can permently damage the aircraft.

Correct

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#223

Post by geofft »

aaron695 wrote: post #200
ummonk wrote: post #140

Earlier quoted context omitted.

Why is that getting downvoted? What the heck.

> knowing some greedy bunch of assholes were effectively that malevolent entity, whose will was expressed via the aircraft. If this it true then link? When was this confirmed? Who are the assholes? Else this is just Reddit spam that contributes less than nothing.

The "greedy bunch of assholes" are the Boeing execs who optimized for profit over the lives of those pilots and their passengers. (I thought that was pretty clear from the comment, fwiw.) I think it's been pretty thoroughly established at this point that an underlying design constraint in the MCAS was that it was easier for Boeing to get a 737-with-modifications approved than a new airplane, despite the engines being configured rather differently from existing 737s, and the MCAS was a computerized hack to avoid instability caused by the design of the newer engines (specifically, the newer engines would risk pitching up and stalling if you flew a 737 MAX like a normal 737, so they added the MCAS to counteract that, and the problem in both crashes was the MCAS unnecessarily activated and pitched the plane down when the plane was actually flying fine). Certainly lots of other things went wrong too, but had they instead just built a new plane design, the problem wouldn't have arisen in the first place. (I can find links about this if you're curious but it seems to be the consensus interpretation of what happened.)

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#224

Post by hacker_9 »

aaron695 wrote: post #200
ummonk wrote: post #140

Earlier quoted context omitted.

Why is that getting downvoted? What the heck.

> knowing some greedy bunch of assholes were effectively that malevolent entity, whose will was expressed via the aircraft. If this it true then link? When was this confirmed? Who are the assholes? Else this is just Reddit spam that contributes less than nothing.

You are disgusting

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#225

Post by aeternus »

> From 05:40:42 to 05:43:11 (about two and a half minutes), the stabilizer position gradually moved in the AND direction from 2.3 units to 2.1 units. During this time, aft force was applied to the control columns which remained aft of neutral position. The left indicated airspeed increased from approximately 305 kt to approximately 340 kt (VMO). The right indicated airspeed was approximately 20-25 kt higher than the left.

This part is very interesting. This aircraft nose down (AND) trim occurred while the electric trim system was disabled. This means that either the pilots were moving the manual trim wheel in the wrong direction, or that aerodynamic forces were causing significant AND trim.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#226

Post by swhitt »

cjbprime wrote: post #95
kayfox wrote: post #88

Earlier quoted context omitted.

> It's possible that aerodynamic load (of the stabilizer opposing the elevator) made it physically impossible to manually trim given any mistrim at the time the cutout happened, given the airspeed they had. Its been noted in previous discussions that while it would be difficult, the load can be overcome if both pilots were to operate the manual trim wheel at the same time. Not that its a good situation to be in.

> Its been noted in previous discussions that while it would be difficult, the load can be overcome if both pilots were to operate the manual trim wheel at the same time. I haven't seen that noted anywhere, and have seen it theorized as impossible without motor assist, given their airspeed and with the elevator opposing. Got a link?

Manual Stabilizer Trim

Excessive airloads on the stabilizer may require effort by both pilots to correct the mis-trim. In extreme cases it may be necessary to aerodynamically relieve the airloads to allow manual trimming. Accelerate or decelerate towards the in-trim speed while attempting to trim manually.

https://www.pilot18.com/wp-content/uploads/2017/01/B737NG_FC... page 312 (8.16)

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#227

Post by na85 »

ummonk wrote: post #140
rdiddly wrote: post #119

Reading through the chronology in section 1.1, it feels like a movie where the aircraft is a malevolent entity that's trying to kill them. So if I were in the cockpit I'm sure it would've been some mix of fear and anger. My life's not in danger though, so I'm only left with the anger, on their behalf, knowing some greedy bunch of assholes were effectively that malevolent entity, whose will was expressed via the aircr…

Why is that getting downvoted? What the heck.

On HN you can say the same things you say anywhere else but GP didn't couch his rant in fancy synonyms and misused Latin phrases like a priori.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#228

Post by treis »

msbarnett wrote: post #184
treis wrote: post #164

Earlier quoted context omitted.

But high enough to re-enable a system you know is malfunctioning? I guess we will have to wait for the final report but the pilot's actions are perplexing here. Even if we accept that they can't trim with the wheel, why enable electric trim and then not use it? Why not enable it, trim to where you want, and then use the cut out switch again?

> But high enough to re-enable a system you know is malfunctioning? They couldn't land with the stabilizers mis-trimmed. If the wheel wouldn't budge, re-enabling it and trimming electronically was the only option likely to occur to them, since the only other possible option (release the column, let the plane nose down so that the forces on the screw ease and they can trim manually) is completely counter-intuitive and…

>They couldn't land with the stabilizers mis-trimmed. If the wheel wouldn't budge, re-enabling it and trimming electronically was the only option likely to occur to them, since the only other possible option (release the column, let the plane nose down so that the forces on the screw ease and they can trim manually) is completely counter-intuitive and was removed from Boeing's documentation and simulator training 30-40 years ago and was not covered in the FAA/Boeing MCAS directive.

They could have just kept flying. They weren't in any immediate danger and had time to reach out for help. Worst case scenario, you fly straight for the next 30 minutes while ascending to 20-30k until you figure out what's going on.

>They did use it after re-enabling it.

Not really. The barely blipped it. Not what I would expect if they had a clear intention to re-enable electric trim in order to get the trim to where they wanted it.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#229

Post by thatoneuser »

Rooster61 wrote: post #105
daddylonglegs wrote: post #96

Earlier quoted context omitted.

> > They must cut it at a moment where the stabilizer isn't grossly mistrimmed with respect to level flight, OR they may well need to re-engage it and race the MCAS to get into a close-to-proper trim setup prior to cutting out the stabtrim and assuming manual trim control. > All while keeping the plane in the air, reading the manual, and attempting not to lose composure knowing that the same thing has happened to ano…

I don't remember where I read it, but my understanding is that the MAX simulator does NOT simulate MCAS behavior. EDIT: Found it: https://www.reuters.com/article/us-ethiopia-airplane-simulat...

I need to stop reading this story until the dust settles because I've read too many outrageous things about this whole deployment...

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#230

Post by darkpuma »

Zak wrote: post #26

The design of this system, from what I've heard so far sounds insane . For some background, systems intended to automatically override pilot input upon detecting an impending stall have been used on large, complex aircraft for a long time. The most common mechanism is a stick pusher, which mechanically pushes forward on the stick to mimic what a pilot should do about an impending stall. The force of a typical stick p…

> "A stick pusher, or a pilot pushing forward on the stick is not enough for the aerodynamics of the 737 MAX in certain circumstances. The position of the engines means the thrust tends to push the nose up, and at low speed, the elevator controlled by the stick alone is not enough to push the nose down when nearing a stall. Instead, the trim must be used, which moves the whole horizontal stabilizer rather than just the elevator. That's not part of the procedure on most aircraft, including other 737s, so regulators would not allow pilots rated for 737s to easily transfer their rating to the new aircraft, if they were willing to certify such an aircraft at all."

I believe this is incorrect. From what I understand, the 737 NGs and 737 MAXes both pitch up when thrust is increased and both may need to be trimmed back to counteract this. The reason MCAS is there is because the characteristics of the MAX are different from NG (that is, the airspeeds and angles of attack at which particular trims are required have changed), making the MCAS system regulatorily necessary, not mechanically necessary. Because either the MAX needs a system that emulates the handling of the NG, or pilots need to be trained specifically for the MAX, and the former is cheaper.

In other words the MAX is not objectively mechanically worse, but rather objectively mechanically different.

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