Boeing 737 Max8 Aircraft Crashes and Investigations [Part 2] 44

[Alistair_Heaton]

This thread is a continuation of:

thread815-445840


****************************
Another 737 max has crashed during departure in Ethiopia.

To note the data in the picture is intally ground 0 then when airborne is GPS altitude above MSL. The airport is extremely high.

The debris is extremely compact and the fuel burned, they reckon it was 400knts plus when it hit the ground.

Here is the radar24 data pulled from there local site.

It's already being discussed if was another AoA issue with the MCAS system for stall protection.

I will let you make your own conclusions.

 

[BrianPetersen]

If the plane is acceptably flyable without MCAS then why does MCAS exist?
If the plane is not acceptably flyable without MCAS then what bad things will happen with it turned off?

 

[waross]

A challenge to Boeing and the FAA:
When the first simulator is programed to simulate a failed MCAS on a 737 MAX8, send a few dozen pilots who have had the present MAX8 upgrade training and see how many of them can handle a failed MCAS during take-off.
I suggest that one failure is one too many.
I suspect that there will be more than one failure.
Then, Boeing and the FAA execs, do not pass Go......

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Alistair_Heaton]

you can't turn it off. the only way you can kill it is by turning off the electric trim system.

The aircraft would not pass certification without MCAS

And there is one sim in the world with MCAS simulated. that's Boeings one.

 

[LittleInch]

There are a few posts here that keep talking about turning the MCAS off.

You can't turn it off and don't even know whether it is the issue or not. There's no alarm or light or anything that I've heard to say MCAS active.

The only thing the poor pilot can do is turn off the electric power to the motor on the elevator trim. However if the system has already commanded a nose down and then you turn the power off you need to manually wind the trim back which could take several thousand feet of air you don't have.

Also MCAS is a required safety feature which is designed to stop a stall occurring dye to the lift being generated by these new engine nacalles. Turn off the elevator trim motors on take off and you can't trim the aircraft for climb and you risk a stall.

I don't know if the MCAS takes in other data like air speed or just the AoA sensor so even the (optional) AoA disagree light might not alert a pilot to the operation of this "hidden" piece of software if it uses other data. The ET pilot apparently reported air speed indicator issues but we will need to see the FDR info to be sure.

So basically Boeing are in a complete pickle on this. Their relative silence is deafening.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Alistair_Heaton]

you can manually trim which is not that onerous because you set the trim before departure.

the recovering trim from full forward manually is the issue. Once its back to something sensible you can fly it no problems manually.

Nobody outside boeing seems to have a clue what data sources it uses.

 

[thebard3]

Reported on AVweb;

'According to reports, Boeing is set to confirm changes previously reported as considered, which include: changing the MCAS configuration to accept data from both angle-of-attack sensors rather than just one; limit the number of times MCAS can drive the stabilizer to affect nose-down pitch; and limit the duration of the events to 10 seconds. Preliminary reports from both the Lion Air and Ethiopian Airlines accidents suggest that MCAS continually tried to offset the pilots’ efforts to level the aircraft. In addition, new coding will make MCAS disengage if it sees a differential in AOA sensor readings of more than 5 degrees.'

Brad Waybright

It's all okay as long as it's okay.

 

[TenPenny]

I read an interesting article today that the only place MCAS is mentioned by name in the 737MAX manuals is in the Glossary. Other than that, the system is not referred to at all.

Was it deliberately left out so that training could be simplified? That seems to be the implication.

 

[John2025]

Although turning off MCAS and manually trimming is obviously the best course in a malfunction, even if it's ideally trimmed it's going to leave the plane with the original tendency to stall at high AoA as depicted in the graph AH posted March 19. I wonder how easy it is to stall this plane without MCAS.

 

[saikee119]

Is everybody looking for just a temporary or a permanent fix to the MCAS?

In the submission for the airworthiness certification Boeing had the stability trim of 0.6 degree per activation but the subsequent AD released after the first crash in Indonesia the stability trim has been quoted 2.5 degree or more than 400%. It was understood that the increase was needed and after proven by the flight tests. The New York Times has reported today in the 737 Max simulator tests the pilot has only a 40 second window to avert the disaster using the existing MCAS settings.

Boeing now says in the new patch the trim will be reduced and becomes a once-only event for 10 second.

Also in the new fix the signals from two instead of one AoA sensors will be used. There is a suggestion that MCAS will not be activated if a fault is found in the AoA sensor system. If this is true and judging by the previous events then it would not be uncommon for a 737 Max to fly without the MCAS for the whole journey.

Don’t these reduction or withdrawal of the MCAS make the 737 Max less safe in the event of nose up created by it higher engine position during operation?

Is Boeing doing a trial and error procedure with the human lives? If this doesn’t work we can always do another fix.

Seem to me Boeing has to come clean to tell the public why the original setting was necessary as over 300 lives have been sacrificed because of it and why the new fix would be able to make the plane safe enough to return to commercial services.

 

[VEBill]

Interesting:

Seattle Times

The limit of the system’s authority to move the tail applies each time MCAS is triggered. And it can be triggered multiple times, as it was on the Lion Air flight.

One current FAA safety engineer said that every time the pilots on the Lion Air flight reset the switches on their control columns to pull the nose back up, MCAS would have kicked in again and “allowed new increments of 2.5 degrees.”

“So once they pushed a couple of times, they were at full stop,” meaning at the full extent of the tail swivel, he said.

Peter Lemme, a former Boeing flight controls engineer who is now an avionics and satellite-communications consultant, said that because MCAS reset each time it was used, “it effectively has unlimited authority.”

 

[saikee119]

In this report based on New York Times investigation with simulator tests it was reported the pilot has a 40 second window to rescue the plane from the nosedive generated by the old MCAS settings. The new proposed setting to be implemented apparently has proved satisfactory in the simulator tests.

Peter Lemme web page today also quotes from a Seattle Times report an ex-Boeing engineer working with the Max plane hinted if MCAS were made known to the pilots then training would have to be provided for them to know the system and how to cope with it. Also if two AoA sensors were used in the MCAS the display and the procedure to deal with the malfunction would necessitate the training to be done in a simulator.

Apparently even Boeing's own pilots who flew Max did not know MCAS.

It now makes sense why MCAS was not made known to the pilot or the purchaser or in the Max's flight Manual.

I wonder if Boeing is watching Peter Lemme's web pages as they are implementing his key recommendations in the coming new fix.

 

[IRstuff]

So Boeing now has a software fix:

https://www.reuters.com/article/us-...asy-to-upload-harder-to-approve-idUSKCN1R72LB

They just need to get it through hundreds of eyes around the world.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

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[charliealphabravo]

I wonder if they are standing by the original sales pitch for the patch as a "software enhancement...designed to make an already safe aircraft even safer”.

Edit: Marketing lies about teeth whiteners and bottled tap water is one thing. There's little chance that Boeing knows anything now that they didn't already know 6 months ago, and yet they spun this as an "enhancement". This decision should be part of the dialog.

 

[thebard3]

Hmmm. I wonder what various regulatory agencies think they mean when they declare that they will 'review' the software changes prior to allowing the planes to fly again. Verification that the new patch has the intended effect is one thing. Combing through the computer code is another, as one program routine presumably has numerous effects throughout others. Windows patches download and install routinely, often even without our knowledge. We never question the effectiveness of them, rather we just assume that Microsoft knows what they are doing. Of course, a computer crash is a much different thing.

Brad Waybright

It's all okay as long as it's okay.

 

[Lou Scannon]

Very disturbing facts coming to light...
While the early Comet breakups can be attributed to ignorance (of metal fatigue design techniques), the word that comes to mind here is negligence, wilful at that.

Maybe the solution is to use higher landing gear and put the engines in a position that does not need MCAS.

In other words, bring back the 757?



"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[VEBill]

...the pilot has a 40 second window to rescue the plane...

40 seconds is not really much different than the 35 seconds pilots' allowed "reaction time" made famous in the movie 'Sully' (*).

So with that assumption, that'd leave perhaps 5 seconds to perform all the required post-reaction tasks.


* Wiki extract for convenience: "The NTSB used flight simulators to test the possibility that the flight could have returned safely to LaGuardia or diverted to Teterboro; only seven of the thirteen simulated returns to La Guardia succeeded, and only one of the two to Teterboro. Furthermore, the NTSB report called these simulations unrealistic: "The immediate turn made by the pilots during the simulations did not reflect or account for real-world considerations, such as the time delay required to recognize the bird strike and decide on a course of action." A further simulation, in which [highlight #FCE94F]a 35-second delay was inserted[/highlight] to allow for those, crashed.[report:50] In testimony before the NTSB, Sullenberger maintained that there had been no time to bring the plane to any airport, and that attempting to do so would likely have killed those onboard and more on the ground."

 

[saikee119]

I wonder if they are standing by the original sales pitch for the patch as a "software enhancement...designed to make an already safe aircraft even safer”.

I am disturbed by it too. Can't he say it makes a dangerous plane less risky? The damn thing kill over 360 people already. The suggestion that "the patch makes an already safe plane even safer" is a total detachment from reality.

It is obvious to many that Boeing knew the problem and how to fix it when the first plane dropped in Indonesia. They could have saved their lives by telling the pilots the existence of the MCAS.

 

[VEBill]

I wonder what various regulatory agencies think they mean when they declare that they will 'review' the software changes...?

Presumably they mean IAW DO-178, perhaps Rev B.

'Software Considerations in Airborne Systems and Equipment Certification'

 

[waross]

So, the engines were changed and unacceptable flight characteristics was an unintended consequence.
The aircraft could stall. To be fair, neither of the crashed planes stalled.
So now with new software and twin AoA sensors, the MCAS may be disconnected or disabled automatically.
Now the aircraft may unexpectedly stall if there is a problem with the MCAS.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

hemi; The point of the MAX was to avoid the huge expense of an airline requiring a second aircraft training track.

saikee119; You're getting a bit shrill.



Keith Cress
kcress -

http://www.flaminsystems.com