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Ethiopian Airlines 737 MAX Investigation Preliminary Report

ecaa.gov.et

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Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#251

Post by VBprogrammer »

cjbprime wrote: post #231
geofft wrote: post #223

Earlier quoted context omitted.

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…

Agree on the consensus. There's a piece of additional flavor, which is that as I understand it Boeing proposed building a new type of plane as an a320neo competitor, and the airlines announced that they'd only buy it if it's a 737 subtype to avoid having to retrain their pilots. It's not just "Boeing doesn't want to pay for certifications", but also -- and perhaps primarily -- "Airlines don't want to pay for training…

Just to add an extra element to what you've already said. It's quite likely that the pilots themselves would have been reluctant to accept another entry level narrow body jet. In the current climate it's often the pilots themselves who are paying for the type rating, at least the first one they acquire.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#252

Post by swhitt »

cjbprime wrote: post #234
swhitt wrote: post #226

Earlier quoted context omitted.

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)

To be clear, that's a link that agrees with me that it can be impossible, not a link that says they just needed to work harder. It's also from a 20 year-old manual, and isn't present on newer manuals, and pilots haven't trained on it in decades. Not appropriate to expect pilots to know, and possibly not helpful here: the pilots were low altitude, so allowing the nose to drop even further (to relieve aerodynamic load)…

https://www.satcom.guru/2019/04/stabilizer-trim-loads-and-ra... does a pretty good job of summarizing it I think. It sounds incredibly difficult to do.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#253

Post by alvah »

cjbprime wrote: post #237
toss1 wrote: post #235

Earlier quoted context omitted.

They would be the set of assholes who: 1) decided to move the engines forward making the aircraft dynamically unstable, but improve performance and potential sales 2) decided to counter the instability with a software system (MCAS) based on a single sensor, with zero redundancy or fail-safe mode, AND make a second sensor an optional extra cost for the airlines, AND bury the whole thing in a poor UI, in short: cheapin…

> AND make a second sensor an optional extra cost for the airlines This would be extremely egregious, but it's not what happened. Every MAX has two AoA vanes. Every MAX only hooks up the MCAS to one vane. The optional feature was just an "AOA disagree" light and display, which wasn't even hooked up to an error alarm. It's a red herring for these crashes, in my opinion. The pilots aren't going to hunt around the cockp…

They could have had "check for AoA disagree" as part of the pre-flight checklist though - I read somewhere that in at least 1 of the MAX crashes, the AoA vanes disagreed on the ground before departure.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#255

Post by bbojan »

tuna-piano wrote: post #238
davepage wrote: post #43

Earlier quoted context omitted.

It does not appear to be "precisely" the procedure, in that sufficient nose up trim was not selected by the yoke manual trim switch prior to pulling the trim cutouts. And then they did not work the mechanical trim wheel hard enough to reset the residual nose down trim. And, the crew left the power setting at climb throughout almost the entire sequence, so they oversped the airframe. And, when they (against procedure)…

Just to put their "mistakes" in context - Sully, America's favorite hero pilot, accidentally put his airplane into an almost stall as he was performing the Miracle on the Hudson (due to the A320's design philosophy, the airplane prevented the stall...). It goes to show- even great pilots doing good work in a stressful time can make critical oversights.

Do you have a reference for that statement?

Because the story that I heard is that he purposefully commanded max pitch knowing that alpha protection would prevent the airplane from stalling, as his landing speed would be lowest at max AoA.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#256

Post by tlb »

alvah wrote: post #253
cjbprime wrote: post #237

Earlier quoted context omitted.

> AND make a second sensor an optional extra cost for the airlines This would be extremely egregious, but it's not what happened. Every MAX has two AoA vanes. Every MAX only hooks up the MCAS to one vane. The optional feature was just an "AOA disagree" light and display, which wasn't even hooked up to an error alarm. It's a red herring for these crashes, in my opinion. The pilots aren't going to hunt around the cockp…

They could have had "check for AoA disagree" as part of the pre-flight checklist though - I read somewhere that in at least 1 of the MAX crashes, the AoA vanes disagreed on the ground before departure.

Are they expected to agree when there's no airflow? What direction should they be pointing in?

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#257

Post by acqq »

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…

They followed Boeing instructions (provided in the report, Appendix 2, and also here: https://theaircurrent.com/wp-content/uploads/2018/11/B737-MA... ).

Note IAS DISAGREE alert:

"In the event of an uncommanded horizontal stabilizer trim movement, combined with any of the following potential effects or indications resulting from an erroneous Angle of Attack (AOA) input, the flight crew must comply with the Runaway Stabilizer procedure in the Operating Procedures chapter of this manual:

- Continuous or intermittent stick shaker on the affected side only.

- Minimum speed bar (red and black) on the affected side only.

- Increasing nose down control forces.

- IAS DISAGREE alert.

- ALT DISAGREE alert.

- AOA DISAGREE alert (if the option is installed)"

About which was written here:

https://leehamnews.com/2019/04/03/et302-used-the-cut-out-swi...

"the high speeds observed" ... "were logical. It’s a consequence of following the Emergency checklist for “IAS disagree” (IAS is Indicated Airspeed, i.e. the dynamic air pressure experienced by the aircraft) after takeoff."

In short, seeing that Boeing indeed wrote about the IAS alert being activated when the sensor fails, and MCAS gets activated, I can only conclude that Boeing indeed knew that the pilots would make the plane uncontrollable if they followed Boeing's instructions. It seems they just gambled on the chance that the second crash won't happen so soon after the first.

Either that, or we'd have to believe that what a single pilot manage to do for his Youtube video a company which is to deliver the planes in worth of hundreds of billions (!) of USD wasn't able to do.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#258

Post by cjbprime »

tlb wrote: post #256
alvah wrote: post #253

Earlier quoted context omitted.

They could have had "check for AoA disagree" as part of the pre-flight checklist though - I read somewhere that in at least 1 of the MAX crashes, the AoA vanes disagreed on the ground before departure.

Are they expected to agree when there's no airflow? What direction should they be pointing in?

You're right, they're literally vanes on the side of the aircraft, they don't do anything without airflow. Takeoff roll is when you could possibly first notice it.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#259

Post by davepage »

cjbprime wrote: post #71
davepage wrote: post #43

Earlier quoted context omitted.

It does not appear to be "precisely" the procedure, in that sufficient nose up trim was not selected by the yoke manual trim switch prior to pulling the trim cutouts. And then they did not work the mechanical trim wheel hard enough to reset the residual nose down trim. And, the crew left the power setting at climb throughout almost the entire sequence, so they oversped the airframe. And, when they (against procedure)…

> sufficient nose up trim was not selected by the yoke manual trim switch prior to pulling the trim cutouts The EAD/service bulletin doesn't talk about sufficient nose up trim or caution against performing the cutout with even a slight mistrim. > And then they did not work the mechanical trim wheel hard enough to reset the residual nose down trim. It's possible that aerodynamic load (of the stabilizer opposing the el…

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 ..."

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#260

Post by YZF »

toss1 wrote: post #235
aaron695 wrote: post #200

Earlier quoted context omitted.

> 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.

They would be the set of assholes who: 1) decided to move the engines forward making the aircraft dynamically unstable, but improve performance and potential sales 2) decided to counter the instability with a software system (MCAS) based on a single sensor, with zero redundancy or fail-safe mode, AND make a second sensor an optional extra cost for the airlines, AND bury the whole thing in a poor UI, in short: cheapin…

Add to that the handling of the complaints about the system, handling of the first crash... The plane should have been grounded after the first crash and possibly some mitigating action should have been taken before that as well. There's going to be a final report and presumably this is far from the end of this story.
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