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Ethiopian Airlines 737 MAX Investigation Preliminary Report

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Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#301

Post by verytrivial »

msbarnett wrote: post #264
davepage wrote: post #259

Earlier quoted context omitted.

The Boeing/Ethiopian ETH-2 bulletin quoted in the above linked AAIB preliminary report on page 33 says "Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT ..."

> Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT .. Which really under explains the situation. In reality the STAB TRIM CUTOUT must be switched to CUTOUT within 5 seconds of using the electronic stabilizer trim, or the MCAS will re-establish the forces.

Wow. This sub-thread is making the images of the grounded MAXs look a whole lot less like an overabundance of caution. If accurate this failure dynamic sounds more like some nasty boss at the end of an escape room game than standard fault diagnostics.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#302

Post by makomk »

sctb wrote: post #28
treis wrote: post #2

This shouldn't be marked as a dupe since it's the actual report. It sounds like they did everything right. There are two fateful moments: >At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied that the trim was not working and asked if he could try it manually. The Captain told him to try. At 05:41:54, the First-Officer replied that it is not working At this point t…

The report was the basis for this article and discussion yesterday: https://news.ycombinator.com/item?id=19570378 . From Hacker News' perspective, since the report itself was prominently linked in the article and its contents were discussed directly in the thread many times, it qualifies as a duplicate.

The report wasn't prominently linked in that BBC article when it was posted here yesterday, because it hadn't been released yet.[1] It was edited into the article at around the same time the direct link was posted to HN. Also, all of the discussion of its contents on that thread seems to have happened after the comment complaining about this thread being marked as a dupe of it.

[1] https://web.archive.org/web/20190404163122/https://www.bbc.c...

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#303

Post by msbarnett »

VBprogrammer wrote: post #192
msbarnett wrote: post #75

Earlier quoted context omitted.

> And, the crew left the power setting at climb throughout almost the entire sequence, so they oversped the airframe. I believe that's correct given that they had an Unreliable Airspeed Indicator warning (due to the malfunctioning AoA sensor), per the memory items on the UAI checklist. It makes the forces on the trim wheel much worse, which explains why they couldn't turn it, but it's the correct checklist response t…

> I believe that's correct given that they had an Unreliable Airspeed Indicator warning (due to the malfunctioning AoA sensor), per the memory items on the UAI checklist. The idea that a pilot would knowingly leave thrust at climb power while in modestly level flight at low altitude and expect not to overspeed is very strange to me, checklist or no checklist. I think they were too busy fighting the controls to worry…

Setting it to climb is literally a memory item, pictured here: https://aviation.stackexchange.com/questions/24739/what-is-t.... That’s pitch 5 degrees up, thrust at climb at their altitude.

Why? Because your instruments disagree about your airspeed. You want to have a large margin to keep your speed high enough that you won’t accidentally stall while you try to establish what’s reliable.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#304

Post by calecon323 »

Rooster61 wrote: post #7

> The crew performed runaway stabilizer checklist and put the stab trim cutout switch to cutout position and confirmed that the manual trim operation was not working. This is very damning to Boeing. It's precisely the procedure they prescribed and intended to mitigate possible MCAS caused trim runaway. In light of the fact that they put this in place as a justification for moving the engines forward without reclassif…

Except they didn't "follow procedure." MCAS trimmed down repeatedly on one instance for 9(!) seconds and yet the pilots waited 3 seconds longer to counteract that with an electric trim up command on the yoke. The procedure is not 1. Let MCAS do its thing 2. Pull back on the stick 3. Hit the stab trim cut off when you have had enough. Attempting to counteract the the trim down command with manual trimming commands should occur continuously "as needed." If you don't attempt to override the trim runaway with manual trim up commands on your control yoke you aren't following the checklist. On the 737 you can see the trim wheels move and if unintended follow the checklist.

The pilots didn't do that at all. Sustained manual trim only occurred after MCAS kicked in again at 5:40:27 and the pilots still waited before invoking the trim up command. The pilots never invoked sufficient trim up to counteract the automatic trim down command. Again, there is a reason the trim controls are on the control yoke in the first place. Of the three major MCAS trim down commands the pilots only stopped the second one with manual commands after it had already pushed the nose dangerously low. If the pilots had simply invoked manual trim promptly and counteracted the erroneous trim manual trim would have been successful after invoking a STAB CUT out.

If you think the pilots are following procedure why at 05:41:46 did: "the Captain ask[ed] the First-Officer if the trim is functional." ? That doesn't make sense, of course the trim doesn't work, the STAB TRIM cut out switches were engaged! But the response by the first officer was that "The First-Officer [has] replied that the trim was not working and asked if he could try it manually." which again doesn't make sense. But it gets worse because this happened a FULL MINUTE after the stab cut out switch was engaged, which means that neither pilot tried to manually trim the aircraft during that time at all!

But it gets better: "At 05:40:27, the Captain advised the First-Officer to trim up with him. " Which again doesn't make sense because it wouldn't make any difference if the both pilots were trimming up or not, the stabilizer doesn't move any faster.

My conclusion is that the pilots didn't know the checklist but its hard to tell because the CDR isn't presented completely.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#305

Post by upofadown »

rootusrootus wrote: post #112
dsfyu404ed wrote: post #20

Earlier quoted context omitted.

Likewise had Boeing designed a control surfaces system such that the pilot always has more control authority than the trim this also would not have happened. I didn't say that MCAS wasn't the lions share root cause here. It's just not as simple as the "hurr durr, MCAS bad" that a lot of people keep trying to portray the more nuanced statements of various regulatory agencies as being equivalent to. MCAS might be bad b…

Are there any airliners from any manufacturer where the pilot always has enough authority to override full trim?

Airbus just gives you a joystick with no force feedback at all. So yes ... but an entirely different philosophy. You tell the aircraft what you want it to do and it figures out how to do it. I suppose these recent events could be used as an argument against the idea of doing essentially fly by wire but then putting in a whole lot of extra stuff to make it seem that you are not doing fly by wire.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#306

Post by teh_klev »

I usually enjoy HN discussions, but this is a pitiful and sad thread. I couldn't be bothered trawling past the responses to the top comment with back seat drivers, and "ooh but I read the 737's flight manual, they fucked up".

Likely 99% of the commentariate here are neither 737 Max pilots, let alone even licensed to fly commercial passenger jets, or even have a pilots license. And no, as much as I love the guy, watching Mentour Pilot does not make you an expert. They have fuck all knowledge about, or even experience, about the sudden cockpit workload that was imposed on these pilots until the point of hull loss. Have some respect. Oh, and you know what, this was Ethiopia's national carrier, I expect these flyers were at the top of their profession and as good a pilot as any other national carrier,

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#307

Post by bronco21016 »

teh_klev wrote: post #306

I usually enjoy HN discussions, but this is a pitiful and sad thread. I couldn't be bothered trawling past the responses to the top comment with back seat drivers, and "ooh but I read the 737's flight manual, they fucked up". Likely 99% of the commentariate here are neither 737 Max pilots, let alone even licensed to fly commercial passenger jets, or even have a pilots license. And no, as much as I love the guy, watch…

Can’t upvote enough. As someone who actually does fly airplanes for a living it’s disturbing to me the amount of ‘expert’ arm chair quarterbacks that have come out on HN in the wake of these two incidents. Immediately after the Ethiopian crash there were 200+ comment threads every few hours full of experts speculating about all the things that went wrong. People who were flat out wrong could not be told otherwise. I had to stop even engaging.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#308

Post by jellicle »

linuxftw wrote: post #158
rootusrootus wrote: post #120

Earlier quoted context omitted.

Blaming the sensors seems pretty plausible, because the expected failure rate of that sensor is roughly 1:100000 and there have been about a quarter million 737-MAX flights since the plane was introduced.

But I just quoted 3 other sensors were reading off so...?

The problem is all those other things are CALCULATED values off the AoA sensor.

Literally everything depends on a single tube which is known to get clogged with ice, bugs etc.

So for the 737 Max, a single clogged AoA sensor causes all these things immediately and simultaneously:

-- all your airspeed and altitude readouts go haywire, at least on one side of the cockpit

-- a bunch of alarms start going off and a bunch of lights start flashing, each indicating a different problem

-- your control stick starts shaking

-- a little-documented system immediately commands the nose straight down into the ground, and keeps commanding it until turned off (but turning it off effectively prevents you from counteracting the nose down command)

Good luck.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#309

Post by tyingq »

refurb wrote: post #281
geofft wrote: post #268

Earlier quoted context omitted.

That's fair, but also, salaries for pilots are not great, and Boeing's former CEO got a salary of $865K/year + $1.3M/year bonus + stock and now that he's retired gets a pension of $730K/year. I'm sort of curious what exactly it would have cost Boeing to say, "This is not a 737, but we will pay to retrain any 737-trained pilot who's interested." (Which still would have given them a negotiating advantage over Airbus!)

Reading the r/aviation subreddit apparently airline pilot salaries have really improved over the last 5 years.

It's very cyclical. For reasons unknown to me, pilot unions have always negotiated a seniority-based pay scale. Where seniority is only how many years you been at the airline. How much total experience you have doesn't matter just how many years you've been with the airline.

So if you stay with the airline for a long time you move up from first officer to Captain and then as years of seniority add up you start making a lot more.

The trouble is the pilots can't threaten to change jobs because if you move from one airline to another your seniority goes back to zero.

Also if an airline declares bankruptcy, all the union contracts are null and void. The airline then has a ton of leverage because the pilots are all out of work. The pay scale that comes out of bankruptcy is typically very low.

Similar if one airline acquires another airline. The pilots at the acquired airline typically get screwed in the pay scale and seniority calculation.

Also jobs like flying cargo planes or piloting for a commuter airline pay very low wages. It's mostly just the big airlines that pay well.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#310

Post by Zak »

cjbprime wrote: post #186
ls612 wrote: post #161

Earlier quoted context omitted.

If the AoA was truly way too high then insane trim would be required to correct that. MCAS and similar systems came about in response to AF 447 where the pilots entered a high AoA situation and stalled the plane into the Atlantic.

Is it necessarily true that you have to use the stabilizer for MCAS? Would implementing a stick pusher instead fail to avoid some stalls?

It's true in the case of the 737 MAX where the pitch-up moment caused by the engines exceeds the elevator authority in a low-speed, high-thrust situation if the pitch trim is also set too high.

MCAS will evidently work with less maximum nose-down trim than the current version has, as the proposed update places a limit on it.

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