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

[Sparweb]

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

 

[LionelHutz]

https://www.seattletimes.com/business/boeing-aeros...

It would be completely naive to believe that the certification process for any other plane didn't also involve a whole lot of schedule pressure and management pressure.

 

[IRstuff]

I've NEVER been under schedule or cost pressure...





NOT

The whole AR thing was news to me, since I had the DER system was still in place.

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

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[Alistair_Heaton]

No pilot is going to run the unreliable airspeed checklist if they don't have airspeed missmatch flag and P1 and P2 and standby airspeeds are within 5 knots of each other.

I have seem nothing to indicate that there was any deviation between any of the three airspeed indications in either crash.

In general pilots can deal with two on going processes. The third usually kills you.

The amount of conflicting info must have been saturating. Stick shaker going which usually means stick the nose down. Over speed warning going off which contradicts the stick shaker. The egpws giving it whoop whoop pull up terrian terrian. The control forces getting heavier and heavier when you do pull back on the stick.

There we have the killer three all lined up.

 

[LionelHutz]

There were 2 times GPWS made “DON’T SINK” calls when the stabilizer moved nose-down before the cutout switches were thrown, not a continuous call-out and not terrain pull-up.

The airspeed indicators deviated by about 20-25 kt according the report.

Not being able to acknowledge and stop the stick-shaker seems to be about as dumb a feature on the MAX as the MCAS system.

 

[Alistair_Heaton]

If no airspeed mismatch and agreeing with the standby then it's just adding to the conffusion.

 

[Alistair_Heaton]

You have to plan for a pilot to hit this issue having not slept for 18 hours and be on the 6 the flight of the day.

If the information load and trouble shooting capacity is beyond that it will always end with people dead

 

[Alistair_Heaton]

6 knts is the max for a airspeed miss match caution nothing reported on that front.

Its a mandatory master caution abort on takeoff.

I am European trained and get 50 % more yearly SIM time and 100% more ground school than legal mins. And my Boeing 737 classic pilots are the same. None of us are even nearly trained to deal with this crap on takeoff.

 

[Alistair_Heaton]

Btw I have never heard of Vo it means nothing to me. What does it mean?

 

[waross]

"It would be completely naive to believe that the certification process for any other plane didn't also involve a whole lot of schedule pressure and management pressure."
Sure but how much pressure is too much?

In 2016, as Boeing raced to get the 737 MAX certified by the Federal Aviation Administration (FAA), a senior company engineer whose job was to act on behalf of the FAA balked at Boeing management demands for less stringent testing of the fire-suppression system around the jet’s new LEAP engines.

That June he convened a meeting of all the certification engineers in his unit, who collectively agreed with his assessment. Management initially rejected their position, and only after another senior engineer from outside the MAX program intervened did managers finally agree to beef up the testing to a level the engineer could accept, according to two people familiar with the matter.

But his insistence on a higher level of safety scrutiny cost Boeing time and money.

Less than a month after his peers had backed him, Boeing abruptly removed him from the program even before conducting the testing he’d advocated.

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

 

[VEBill]

Vo: maximum operating maneuvering speed

Ref FAA regulations

 

[wayne440]

If you begin to cost your employer significant amounts of time and money, they will do something about it.
Sometimes the squeaky wheel gets the grease, sometimes it is removed and replaced with a ready spare.
If the FAA needs someone to act on their behalf, that person should be an FAA employee.

 

[VEBill]

BBC News item

I believe that this BBC news item is related to the Boeing item that I'd previously posted above (6 May 19 10:27).

 

[LionelHutz]

6 knts is the max for a airspeed miss match caution nothing reported on that front.

Its a mandatory master caution abort on takeoff.

The mismatch certainly was in the report, it mentioned both the 20-25kt speed variation and also a comment that the airspeed, altitude and flight director pitch bar values deviated with the left side values lower than the right side values. No cautions about it were mentioned so either left out or the MAX doesn't give a caution with that much deviation for some reason.

The deviations started after take-off, so no way to abort by then.

 

[LionelHutz]

Sure but how much pressure is too much?

How much caution is too much?

BBC News item

I believe that this BBC news item is related to the Boeing item that I'd previously posted above (6 May 19 10:27).

Is there anything that shows how having the disagree warning would have helped?

 

[Alistair_Heaton]

"The mismatch certainly was in the report, it mentioned both the 20-25kt speed variation and also a comment that the airspeed, altitude and flight director pitch bar values deviated with the left side values lower than the right side values. No cautions about it were mentioned so either left out or the MAX doesn't give a caution with that much deviation for some reason."


So another master caution going off we are up to 4 now.


Those symptoms are usually present in a bird strike. Maybe its a bird strike took out one sides pitot system and AoA vane.

The flight directors are usually split until we are doing an approach and we are locked onto a ILS. Then they link and do the error checking.


Vo... ok its the speed that you can use the full deflection of the controls without damaging the airframe. Takes me back 16 years to when was a FI. But its not the max operating speed. Its usually only defined for light aircraft. And is usually linked to the rudder and tail strength. There are 3 cats Normal, Utility and aerobatic in light single engine aircraft.


Cat A commercial aircraft have lockouts to prevent full usage of the controls in certain configurations eg normally we have 9 deg of rudder when the aircraft is clean. When we select flaps then it goes up to 14 deg. But we can use the full range of controls up to Vmo which is max operating speed when clean. With flaps out then we are limited by the flap speed which takes into account the increase in rudder power.

The max operating speed Vmo may be a structural limit. Or it could be a limit due to transonic flow over part of the aircraft or it could be due to some certifcation limit of testing eg the windscreens for bird strikes.

https://aviationglossary.com/v-speeds/

Are the icao ones for these cat A machines.


The aircraft is protected from the pilots mostly allowing full control usage. What you can't do though is cycle the control inputs. ie use full left rudder then go full right and then back again. This was the reason why the tail fell off the airbus just after 9/11. There are slightly different historical philosophys between US pilot practise in realtion to stalling and upset recovery. US used to teach not more than 100ft height loss in stalling, Europe we try an minimise it but lowering the AoA is more important and preventing secondary stall. Upset they used to teach to use the rudder to pick a wing up using secondary effects.


Basically the dash crash got NASA and the FAA looking at it and they should be teaching the eruopean method now for stalling.


And the airbus tail falling off also got them to change things to the european way of correcting upset using the primary control inputs.


But there are loads of old time instructors and pilots that still use the old US methods and teach them. European pilots that get trained across in the US have to have them punched out of them. If those tendencys are spotted in the sim its a fail.

 

[VEBill]

Would a Disagree Warning help?

Pilot overload can be an issue. So it's a valid point about one more warning.

But it can be argued that the AOA Disagree should automatically disable, or at least apply limits on the actions of, the MCAS.

Why allow MCAS any authority (during AOA Disagree) when there's such high odds that its input is bad?

The science of how aircraft automation and the interface with human pilots, to eliminate 'battles' and ensure optimum synergy, especially in abnormal or emergency situations (when the automation itself may have partially failed), clearly remains an immature field.

Furthermore, it's my opinion that this narrow field is at least 10 years behind where I'd expect them to be. These sorts of incidents, very generally, have been happening since 1988.

It's a subtle topic, and these comment boxes don't really enable a complete dissertation on this. So, apologies in advance for any incompleteness on my part here.

 

[RVAmeche]

Would a Disagree Warning help?

Pilot overload can be an issue. So it's a valid point about one more warning.

But it can be argued that the AOA Disagree should automatically disable, or at least apply limits on the actions of, the MCAS.

Agreed. Considering the authority the program has and only two sensors to potentially read from, if there's a significant discrepancy the software should disable any action and throw an alarm (AoA disagree).

Is this how the optional feature Boeing offered worked? I get the impression it just gave an AoA disagree alert but didn't actually have logic to shutdown MCAS.

 

[itsmoked]

While too many problems can be a problem there is also the case where a human mind is very good at patterns. If all information is provided often a glance at it will distill out in a mind 'the pattern' providing fast recognition of the fundamental problem.

I know most of the time that there isn't enough information to solve complex problems. We cast about over long periods trying to match the symptoms to an already understood and mentally categorized failure. Lacking enough data we have to begin hypothesizing and running logic and real tests to gather more data until the correct neural paths light up with full recognition. The hypothesizing / examination process takes a lot of time. So to me - dish up everything known post-haste to pilots with a problem.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[HamburgerHelper]

How is it that the flight controls are not tested through a battery of situations like monte carlo or some extremely thorough checklist? I have a hard time imagining that there are an unmanageable number of scenarios? Even something like 500-1000 scenarios should easy be testable. It would take time but it is very doable. For two planes to have crashed and at least two reports in the U.S. of this planes behavior, the situation could not have been that odd for so many people to have stumbled into it.

------------------------------------------------------------------------------------------
If you can't explain it to a six year old, you don't understand it yourself.

 

[IRstuff]

I don't think it's as easy to test as people seem to think; these are not discrete event simulator type problems; the exact and entire immediate flight history leads into any specific flight failure condition.

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