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MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures

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MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures

Old 23rd Sep 2019, 19:26
  #2541 (permalink)  
 
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Originally Posted by DaveReidUK View Post
A bit more digging reveals that it's a little more complicated than that. The AOA DISAGREE annunciation worked as intended on the aircraft of operators who had opted for the PFD AoA indicator (a notable example being American Airlines), but was non-functional on aircraft without that option (i.e. most other airlines' aircraft).
That's what I said. It was incorrectly tied to the optional indicator package, so only operated if you had the extra package. It was supposed to be active w/o the package. Simple configuration mistake, probably in the build stage. I don't know how Boeing controls the options. Different software builds would be my guess, but it could be controlled by something similar to a license file. But deactivated code is a pain to certify. Much easier to do build options so the code just doesn't get included.
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Old 23rd Sep 2019, 19:31
  #2542 (permalink)  
 
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Originally Posted by Fly Aiprt View Post
Infrequentflyer, great post !
Indeed what you mention here has been nagging at me for a while.
The MCAS principle doesn't make sense : can't be overridden with the yoke because they say it must stay active, but can be deactivated with pedestal switches...
MCAS doesn't make sense and it's too late now for anyone to say MCAS should be inactivated on the Max, and give the flight envelope where the pilot might notice a non linear response to pitch input. The autopilot is not bothered by the non linear response and the real pilot shouldn't be bothered either. As infrequentflier says, when Boeing/FAA wrote the AD procedure where you cut out MCAS they then didn't warn you about any flight regime to avoid and no guidance about landing as soon as possible.
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Old 23rd Sep 2019, 20:01
  #2543 (permalink)  
 
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Originally Posted by switch_on_lofty View Post
You don't need AoA to fly thrust and attitude.
Technical correction not aimed at the wider arguments.
You make it sound so simple Switch On but there is a minor detail that escapes me in your strategy.

How does one fly thrust and attitude when the attitude can't be controlled?

Last edited by jdawg; 23rd Sep 2019 at 20:25. Reason: Wording
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Old 23rd Sep 2019, 20:24
  #2544 (permalink)  
 
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Originally Posted by etudiant View Post
Challenging when the AoA indicator is on the fritz.
How so, many types does without one and you've got 3 HSI's for reference,
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Old 23rd Sep 2019, 20:40
  #2545 (permalink)  
 
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Originally Posted by ST Dog View Post
The captain didn't do it because of fatigue, it was to look for answers, thinking he's find something the F/O missed. But he wrongly assumed the F/O would continue to counter MCAS like he had been doing. 20-25 seconds later he's pulling harder than the F/O ever did.
(There are still some oddities in the last 40-50 seconds if the trace. Why the split when the F/O took over? Why did the F/O's force drop so much when the captain rejoined him?)
Wasn't aware of this version of the document - or had forgotten it - on Leeham News.
Even without clear units, control column forces seem no trifle, as expected with mistrim, hence the notion of fatigue.

The split between the yokes occurs when one pilots pulls (or push) harder than the other. Posted a drawing of the mechanism long ago.
F/O pull drop : with the aircraft finally doing a bunt, the acceleration goes negative and the pilots are thrown from their seats. If not very tightly restrained, keeping pulling on the yoke might be difficult.
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Old 23rd Sep 2019, 21:00
  #2546 (permalink)  
 
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Originally Posted by jdawg View Post
You make it sound so simple Switch On but there is a minor detail that escapes me in your strategy.

How does one fly thrust and attitude when the attitude can't be controlled?
I agree with your implication that ‘it’s not so simple’.

However; attitude (pitch and roll) information is provided by the aircrafts IRSs. They are the aircrafts sole source of attitude and heading information with the exception of the SBY attitude indicator and magnetic compass.

So - you have attitude indications, and you have thrust. Independent of all of the other stuff that’s trying to lead you astray and confuse you. Including the AOA inputs.

If I misread what you meant by “controlled”. Then disregard
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Old 23rd Sep 2019, 21:45
  #2547 (permalink)  
 
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It's hard to control attitude when you have to increasingly pull lbs of force just to prevent the nose from dropping.
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Old 23rd Sep 2019, 21:54
  #2548 (permalink)  
 
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Originally Posted by DaveReidUK View Post

The AOA DISAGREE annunciation worked as intended on the aircraft of operators who had opted for the PFD AoA indicator (a notable example being American Airlines), but was non-functional on aircraft without that option (i.e. most other airlines' aircraft).
Why in god’s name was this offered as an optional extra?

The second vane was there. The wiring to the FCC was there, the software which compared the two values and outputted an annunciation was there, and it would be presumably just as easy to provide it for all customer options, rather than just some.

We will never know whether such an annunciation on the accident aircraft would have ‘fast-tracked’ the diagnosis of the problem especially on ET where by that time it was known that MCAS existed and it was known that MCAS was triggered by data from an AoA vane.

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Old 23rd Sep 2019, 22:11
  #2549 (permalink)  
 
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Originally Posted by JPJP View Post


I agree with your implication that ‘it’s not so simple’.

However; attitude (pitch and roll) information is provided by the aircrafts IRSs. They are the aircrafts sole source of attitude and heading information with the exception of the SBY attitude indicator and magnetic compass.

So - you have attitude indications, and you have thrust. Independent of all of the other stuff that’s trying to lead you astray and confuse you. Including the AOA inputs.

If I misread what you meant by “controlled”. Then disregard
Yes but you are discussing inputs to control. Read the darn instruments and respond and fly the aircraft. Fair.

The issue here though surely isn't one of control, it's one of command.

If you don't have command of the aircraft, because the automation is overriding your inputs, then regaining command precedes regaining control.
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Old 23rd Sep 2019, 22:16
  #2550 (permalink)  
 
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Originally Posted by OldnGrounded View Post
Yes, i think that's correct.
This is what the alert looks like on the MAX PFD. It’s tiny.



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Old 23rd Sep 2019, 22:19
  #2551 (permalink)  
 
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Originally Posted by Turbine70 View Post
Yes but you are discussing inputs to control. Read the darn instruments and respond and fly the aircraft. Fair.

The issue here though surely isn't one of control, it's one of command.

If you don't have command of the aircraft, because the automation is overriding your inputs, then regaining command precedes regaining control.
WTF ?

At least 10 Characters
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Old 23rd Sep 2019, 22:19
  #2552 (permalink)  
 
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Well (obviously) you can't control attitude if it's not controllable.
My point was that AoA is not an input into attitude or thrust therefore not required to fly using those settings.
If there is a system on the aircraft which is taking AoA and stopping you from selecting and maintaining an attitude (like an errant MCAS) and you can't or don't disable it using the "AoA on the Fritz" drill then you are stuck. I'm doing my CAA mandated pitch training for [737] pilots this week so I'll keep a look out for it.
edited for grammar.
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Old 23rd Sep 2019, 22:30
  #2553 (permalink)  
 
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Afaik, there has not previously been an aircraft control system that forcibly overrode pilot inputs repeatedly, after a brief (6 second) delay.
So I believe it is at best disingenuous to claim inadequate pilot training.
People cannot train for systems that are hidden from view, as was the MCAS.
If fully briefed FAA crews cannot recover the aircraft in simulator flights, I do not believe the average line pilot will do better.
The aircraft as currently configured is not airworthy. Is that so hard to accept?
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Old 23rd Sep 2019, 22:36
  #2554 (permalink)  
 
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Originally Posted by etudiant View Post
Afaik, there has not previously been an aircraft control system that forcibly overrode pilot inputs repeatedly, after a brief (6 second) delay.
So I believe it is at best disingenuous to claim inadequate pilot training.
People cannot train for systems that are hidden from view, as was the MCAS.
If fully briefed FAA crews cannot recover the aircraft in simulator flights, I do not believe the average line pilot will do better.
The aircraft as currently configured is not airworthy. Is that so hard to accept?
No I do accept that and agree with all above.
I don't blame pilot training.
There still isn't an AoA input to Attitude or Thrust though. Which is what I said in my first post.
And specifically said I was not commenting on the wider arguments by doing so.
Edited for clarity.
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Old 23rd Sep 2019, 22:49
  #2555 (permalink)  
 
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Originally Posted by JPJP View Post


I agree with your implication that ‘it’s not so simple’.

However; attitude (pitch and roll) information is provided by the aircrafts IRSs. They are the aircrafts sole source of attitude and heading information with the exception of the SBY attitude indicator and magnetic compass.

So - you have attitude indications, and you have thrust. Independent of all of the other stuff that’s trying to lead you astray and confuse you. Including the AOA inputs.

If I misread what you meant by “controlled”. Then disregard
You did misread or perhaps I lacked clarity. My point was this entire thread is about loss of pitch control. So one cannot simply suggest thrust and attitude be the antidote. You can't control the attitude.

​​​​​By now we all know that if you are so desperate for control that you are resorting to pitch and power (as we call it in the states ) and you lost pitch control you must adjust thrust accordingly. That's where Ethiopian failed.

My employers memory item for that situation, above acceleration altitude but below FL100, is 10 deg pitch and climb detent in the A320. In a situation like Max encountered you can't maintain 10 deg pitch so thrust must be reduced.

Just hate to see others here say the pilots should have simply established a pitch and set a thrust setting.

When you've been there and done that report back on how easy it was please.
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Old 23rd Sep 2019, 22:59
  #2556 (permalink)  
 
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Originally Posted by switch_on_lofty View Post

There still isn't an AoA input to Attitude
Surely that depends on your definition of AoA input?

No, there is no direct relationship between AoA value and attitude, however while MCAS operates, either as it should or under fault conditions it can be said that AoA does have an input to attitude (along with configuration and autopilot on/off selection.)
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Old 23rd Sep 2019, 23:00
  #2557 (permalink)  
 
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Originally Posted by switch_on_lofty View Post
No I do accept that and agree with all above.
I don't blame pilot training.
There still isn't an AoA input to Attitude or Thrust though. Which is what I said in my first post.
And specifically said I was not commenting on the wider arguments by doing so.
Edited for clarity.
As a humble SLF, my question would be 'How does the average Joe Pilot react when his airplane is unexpectedly trimming ever more nose down?'
How can the pilot control attitude when the airplane will not stay trimmed?
It seems much harder imho to resolve this when a part of the mechanism is repeatedly acting independently of (and perhaps contrary to) the controls.
When the system is that far out of bounds, how can the pilot trust whatever thrust or attitude indicators that remain?
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Old 23rd Sep 2019, 23:01
  #2558 (permalink)  
 
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I don't get it, a thrust reduction causes a nose down momentum. With 80% N1 and stabilizer trim for the nose down, you would still overspeed in a short time.
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Old 23rd Sep 2019, 23:14
  #2559 (permalink)  
 
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Originally Posted by Turbine70 View Post

If you don't have command of the aircraft, because the automation is overriding your inputs, then regaining command precedes regaining control.
A technical clarification is in order. At no time did the automation (i.e. MCAS) "override" pilot inputs. Quite the reverse - the pilot actuated Main Electric Trim actually overrode the automation every time it was used. The problem was that MCAS did not stop making inputs after the pilots intervened, and the pilots flying the accident aircraft did not make sufficient Main Electric Trim inputs to compensate for the unwanted MCAS inputs - which BTW, was the key to maintaining attitude control. Why the pilots did not make those stab trim inputs aggressively enough is separate discussion.
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Old 23rd Sep 2019, 23:18
  #2560 (permalink)  
 
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Originally Posted by etudiant View Post
As a humble SLF, my question would be 'How does the average Joe Pilot react when his airplane is unexpectedly trimming ever more nose down?'
How can the pilot control attitude when the airplane will not stay trimmed?
Humble answer: The pilot keeps inputing nose up trim to counter the undesired nose down trim. At some point when the pilot gets tired of repeatedly putting in nose up trim, the pilot deactivates the electric stab trim system and reverts to manual trim.
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