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Boeing 737 Max8 Aircraft Crashes and Investigations [Part 3] 36

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Sparweb

Sparweb

Aerospace
May 21, 2003
5,131
This is the continuation from:

thread815-445840
thread815-450258

This topic is broken into multiple threads due to the long length to be scrolled, and many images to load, creating long load times for some users and devices. If you are NEW to this discussion, please read the above threads prior to posting, to avoid rehashing old discussions.


Some key references:

Ethiopian CAA preliminary report

Indonesian National Transportation Safety Committee preliminary report

The Boeing 737 Technical Site

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF
 
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Alistair_Heaton said:
The airbus didn't kill any pax. And it was a one off.
Click to expand...


The A320 didn't kill anybody?
Air France Flight 296 The stunt with passengers onboard killed 3.

Another poster mentioned AF447. That was a A330 not A320 but it was a over-complex automation caused crash.

What about Indonesia AirAsia Flight 8501? Very similar to AF447. Pilots can fly years in an Airbus without actually knowing how to fly an aircraft. The automation breaks and they crash it.

Airbus can even be a contributory factor in a crash of a Boeing. Asiana Airlines Flight 214 First two times a pilot with years of Airbus flying tries to actually fly an airplane he has the controls yanked from his hands, and the third time he crashes it.

 
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From
Wikipedia said:
Air France Flight 296 was a chartered flight of a new Airbus A320-111 operated by Air France
Passengers 130
Crew 6
Fatalities 3
Injuries 50
Survivors 133 (136 initially)

... three did not escape. One was a disabled boy in seat 4F who was unable to move. Another was a girl in seat 8C, who was unable to remove her seatbelt (her younger brother had removed his own seatbelt but was carried away by the rush of people before he could help his sister). The third was a woman who had reached the front door and then returned to help the girl.
Click to expand...
 
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There's also countless instances of set screw shaft couplings that operate just fine, indefinitely.

The coupling you're describing is subject to very low levels of torque. I suspect if the application called for splines they would be there.

Yet again, we're hip deep in armchair quarterback territory.
 
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Most of the time a setscrew sets against a flat spot or even sometimes a recess in the shaft, which would require a little bit more 'looseness' for it to actually come apart.

Brad Waybright

It's all okay as long as it's okay.
 
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"There are countless references relating to failures of various set screw held devices that are said to have failed due to incorrect tigtening torque."

So, nothing wrong with the setscrews, per se.

TTFN (ta ta for now)
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Satcomguru has a good discussion about the AoA failure:

There are a number of takeaways:
> AoA disagree -- Boeing supposedly has that fixed in the new software
> Absurd AoA reading -- the AoA faulty reading was larger than supportable from other flight parameters; unclear whether anything is being done about absurd data
> Absurd AoA dynamics -- the AoA went from relatively nominal to absurd in such as short timeframe that is patently impossible; again, unclear whether there's anything being done about that.

So, while there might have been a physical hardware/electrical failure in the AoA sensor, what the rest of the aircraft did with the information, in context, was also a massive failure. The logical failure is possibly still unresolved; sometimes, you need to kick everyone involved off the program and start with a completely new set of eyes and brains.

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A justification/excuse for not adding the AoA disagree feature was that it would trigger re-certification.
Dollars over safety again.
Will the fix be re-certified?
Why is this the first 737 to have MCAS?
As I understand it, it is because of unacceptable flight characteristics caused by the location of the Leap engines.
Is anyone else concerned that while MCAS may be meeting the letter of the rules, it is avoiding the spirit and possibly the intent of the rules?

Bill
--------------------
"Why not the best?"
Jimmy Carter
 
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IRStuff - the same problems are lurking in Airbus software no doubt. What control software would let a pilot tear the tail off an airplane or stall one 30,000 feet to the ocean. To do otherwise requires a full dynamics simulator that compares all inputs to a real-time model to see if there's a mismatch.

But what to do when there's an error in the on-board simulator? Maybe independently develop 3 different simulators; but how much tolerance can there be allocated for inevitable differences? And what if 2 of 3 developers misread a portion of the spec and develop a simulation that is actually wrong, potentially voting off the correct one?

I suspect that avoiding an infinite swirl of endless complication is why MCAS used only one AoA indicator - all faults coming from there are handled the same way. Set pitch and power and shut off the stab trim if it keeps trimming in a direction the pilot doesn't want. KISS.

If there's a fundamental problem it is in the training. When Boeing mentioned "continuous" they failed to mention how long "continuous" needed to be evaluated before pulling the plug. Apparently 5 seconds is too long; that's the amount of time the ET pilots let it go before shutting off the trim motors, and long enough to be insurmountable during airspeed runaway by just pulling hard on the yoke. A secondary problem is the false stall warning and stick shaking that distracted the pilots, and their inability to ignore it after a full minute of that nonsense had gone by. I would probably add a check for the actual stab trim as part of pre-flight with a schedule for climb-out.
 
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"And what if 2 of 3 developers misread a portion of the spec and develop a simulation that is actually wrong, potentially voting off the correct one? "

Not a "what if," we had that happen on a relatively tiny project, where we designed a processor and a data recorder reading data from a bus, and a simulator to test them; all designers misread the ICD, so all the hardware worked fine with each other, and the simulator, but crashed on the actual flight system.

But, you point to only one of the issues with the AoA problem; when the AoA data goes faulty, there ought to be something that looks at the data and says, "Gee, that's stupid data, I should ignore it or switch to the alternate AoA sensor."

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"As I understand it, it is because of unacceptable flight characteristics caused by the location of the Leap engines."

But, I don't think that's true; the plane flies fine without MCAS being activated; it's only an issue if the plane is already flying outside its normal mode. It was meant as a safeguard, not as a part of normal operation.

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It seems to me, any way you slice it, it boils down to a top level system engineering failure.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
 
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The departure trim setting is set from the trim details from the load sheet during the before start checks unless you get your final load sheet via ACARs during taxi. If the trim is set outside the normal range when you bring the power levers forward of flight idle by more than 20-30 degs then a config warning will sound. And takeoff is abandoned.

The inability for either the electric or manual trim to be able to trim the aircraft in the event of a 5 second trim runaway is now up for discussion if the whole system meets certification standards whether or not the mcas is fixed to be more fault tolerant

BTW I too have no doubt that airbus has similar gremlins lurking as well in its control software.
 
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IRStuff said:
"As I understand it, it is because of unacceptable flight characteristics caused by the location of the Leap engines."

But, I don't think that's true; the plane flies fine without MCAS being activated; it's only an issue if the plane is already flying outside its normal mode. It was meant as a safeguard, not as a part of normal operation.
Click to expand...

MCAS does exist because of unacceptable flight characteristics- in one very specific area of the flight envelope.

Yes, the plane 'flies fine' without it. But MCAS is a safety system- not a primary flight control system. It was, obviously, not implemented extremely well but that doesn't mean it isn't a necessity on aircraft configured with those engines.
 
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Did not say or imply it wasn't necessary, just that the statement "As I understand it, it is because of unacceptable flight characteristics caused by the location of the Leap engines." was overly broad, and the implications of the more narrower, safeguard, function of MCAS implies a different type of scrutiny than it if was primary flight equiment.

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I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
 
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Does mcas save lives? Are there numbers that show the world is better for having mcas even if it doesn't work the way that it should sometimes?


How come there is no agency like the FAA that certifies "driverless" vehicles? Similar issues have or will come up with these system.

------------------------------------------------------------------------------------------
If you can't explain it to a six year old, you don't understand it yourself.
 
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The electric trim had the ability - the pilots chose not to use it in the same way they chose not to retard the throttles, the first step in several procedures.

How does a pilot not notice the level-flight control force go from 0 pounds to maybe 30-50 pounds and increasing and think, nope, I'm good for the next few hours, no need to trim that out? How do they never look down and see what the trim indication says? This is a fundamental pilot training failure, independent of MCAS.
 
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Those rhetorical questions might just as easily be posed to demonstrate that the actions were surely attempted but were ineffective due to problems with the equipment.

Where are we anyway with the investigation of the two incidents? I only remember hearing about the preliminary report from the second.
 
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"How come there is no agency like the FAA that certifies "driverless" vehicles? Similar issues have or will come up with these system."

There is, the US DOT. The problem is that, unlike the FAA, which has dealt with basically the same stuff for 70 years, DOT hasn't dealt with this subject for more than about 2 or 3 years, and there's zero precedent for the level of validation, particularly when it's 100% software with no analytical validation tools

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