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Ethiopian Airlines 737 MAX Investigation Preliminary Report

ecaa.gov.et

141–150 of 347 posts

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#141
post #54

Earlier quoted context omitted.

A compounding problem is, if the MCAS system is disable, now the flight characteristics are completely changed. Without additional training, there's no way for the pilots to know they have to trim down.

There's no way for pilots to know they have to trim down under what conditions?

During otherwise normal flight conditions, the nose might unexpectedly pitch up. MCAS is designed to prevent that when AoA > somevalue to prevent stalling.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#142

Earlier quoted context omitted.

> they were only 7,000 feet above the ground No, it's worse: the origin airport is at 7000ft elevation. They only had around 1000ft height AGL for all of the flight. So I agree that releasing the elevator at all seems surely suicidal.

They're at 12,000-14,000 feet altitude at 05:43ish, when the co-pilot reports the non-functional manual trim. So ~6,000-7,000 height. Still damn close to the ground to be comfortable letting the plane dive.

Oh! I think this is new information in the report -- the FlightRadar24 ADS-B data never shows them above 8500ft altitude, ~1000ft AGL. FlightRadar24 must have missed the final few minutes?

https://www.flightradar24.com/blog/flightradar24-data-regard...

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#143
post #5

Earlier quoted context omitted.

So MCAS put them in a hard to recover position which required electric trim to recover, and as soon as they turned on the electric trim MCAS turned on again and forced them into a crash? Then this is much worse than initially suggested, it means a pilot can be aware of MCAS and still be put in a extremely dangerous position due to the extreme control authority of the module.

Per the article a combination of things put them in that situation. Not just MCAS. Why is everyone so wedded to the narrative that this is the fault of MCAS and nothing else? Complex systems that have millions of man hours spent making them safer don't usually have back to back failures because of one faulty subsystem. We've incrementally refined commercial air travel to the point where single source accidents are ba…

Sadly, it looks like those millions of man hours of incremental safety refinement also created a false sense of security. That (and management overriding engineering concerns) are the only explanations I have for how MCAS was implemented: because it had to be able to correct the pitch-up tendency of the 737 MAX and stay "invisible", so additional training could be avoided, Boeing apparently chose to use only one AOA sensor as "single source of truth" - because using both would have increased the chance of the system having to deactivate itself, which would probably have made the FAA mandate the additional training that Boeing wanted to avoid. This is just my personal theory however...

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#144

Earlier quoted context omitted.

Why exactly? if Boeing did not updated the manuals and checklists how would pilots know that? from internet forums? Should a pilots ignore the checklists and try steps he read on the internet ? I could not find if Boeing updated their manuals/checklists after the first crash.

Yes, Boeing issued this service bulletin after Lion Air: http://www.avioesemusicas.com/wp-content/uploads/2018/10/TBC... And the FAA made it an emergency airworthiness directive in response. The steps on it were broadly followed by the Ethiopian flight.

Am I missing it because I don't see flaps mentioned anywhere in that link.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#145
post #18
post #3

Indeed looks like they did disable MCAS using the stabilizer trim cutout switches, but the aircraft was trimmed nose down when they did so. Aerodynamic loading prevented manual trimming using the trim wheels. They eventually turned electric trim back on, as they didn't really have any other options, but didn't trim back enough, and left it turned on. At this point the right airspeed indicator (which should be more re…

Yeah, from the report: > At 05:40:35, the First-Officer called out “stab trim cut-out” two times. Captain agreed and First Officer confirmed stab trim cut-out. [...] > 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…

For comparatively trivial things like what to do when we get too much traffic on servers, engineers do “game day” testing.

How does anyone expect pilots to run through these crazy scenarios and perform flawlessly unless they have done it in a simulator many times?

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#146
post #24

> 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…

Just out of curiosity, will there actually be any punishments handed out beyond just a slap on the wrist? Or is Boeing far too large of a corp to take on?

What charges do you recommend? Links to the US code here: https://www.law.cornell.edu/uscode/text

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#147
It appears that Boeing's directive was simply wrong, and doomed them. The right response to faulty MCAS is not to do a stab trim cutout and then manually retrim, but to first use the manual electric trim switches to fix the trim and then immediately do a stab trim cutout. This is mentioned at the end of the directive, but reads more like an afterthought when it should be the standard procedure.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#148

Earlier quoted context omitted.

Yes, Boeing issued this service bulletin after Lion Air: http://www.avioesemusicas.com/wp-content/uploads/2018/10/TBC... And the FAA made it an emergency airworthiness directive in response. The steps on it were broadly followed by the Ethiopian flight.

Am I missing it because I don't see flaps mentioned anywhere in that link.

You're not missing it. The pilots followed the instructions, and the instructions do not mention flaps.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#149
post #54

Earlier quoted context omitted.

A compounding problem is, if the MCAS system is disable, now the flight characteristics are completely changed. Without additional training, there's no way for the pilots to know they have to trim down.

There's no way for pilots to know they have to trim down under what conditions?

I don't understand, either you need the MCAS to fly the plane or you don't.

If a 737 pilot can operate a 737 MAX only with MCAS, then the pilot shouldn't be able to disable it, right? What if he disables it and then the plane is stalling? There is no MCAS to help.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#150
post #17

Earlier quoted context omitted.

I thought all jets had to be capable of performing non powered glides (as in no electrical power, not just engine power). I guess that's no longer a requirement.

The planes when setup correctly have a pretty good glide slope actually. When there is no power the pilots can deploy the apu to restore basic power for flight controls.

The 737 has a better glide ratio than a Cessna 172 when both set up correctly.
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