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

 

[Alistair_Heaton]

http://www.b737.org.uk/mcas.htm#techdes

seems to be a good summary

Also the statement

"Boeing has said in a statement on Monday 29 April that an error on their part meant that the AOA DISAGREE alert was only enabled on aircraft in which the customers had selected the optional AOA indicator. The alert was intended to be enabled on all MAX aircraft as standard.

“The disagree alert was intended to be a standard, stand-alone feature on Max airplanes,” the company said. “However, the disagree alert was not operable on all airplanes because the feature was not activated as intended.”

Note that the MAX will have a software update (CDS BP?) to allow the disagree alert to function without relying on any optional systems as it does on the NG. This of course is in addition to the FCC update for MCAS. "

 

[itsmoked]

Thanks for the A_H update.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[RVAmeche]

How would that alert have worked if you didn't have the optional indicator?

 

[SwinnyGG]

The 'indicator' is not a separate gauge on the panel, it's just a software switch that, when enabled, displays a digital readout on an otherwise blank spot on the primary flight display. Not enabling this option doesn't prevent error reporting on the PFD or elsewhere.

No AoA indicator:

w/ AoA indicator:

 

[LittleInch]

Is that little orange wording at the bottom the AoA disagree that Boeing are talking about or is it supposed to be a separate yellow or red standalone light??

If it's only the words that looks like it could get very easily missed to me if there's all sorts of stick shaking and alarms going off at the same time.

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

 

[debodine]

If I were involved in the design, Instead of the yellow AOA DISAGREE text which is not co-located with the indicator, I think I would prefer something like this, due to the critical nature of angle of attack:

When the DISAGREE condition is sensed, the indicator on the PFD face (which I would consider easier to notice during the PFD portion of the pilot's instrument scan rather than a distant text message) should turn flashing yellow to indicate the condition. Then there would be a pilot acknowledgement (pushing a button, moving a switch, etc.) and after successful acknowledgement, the indicator would stop flashing but would remain yellow.

By remaining in view but yellow, then each pilot could still refer to their own PFD for AOA but would realize that one or both indicators may be in error. If they come to a conclusion that one of them is accurate, then they could agree to use that one good indication for flight path control but the constant yellow would remind them to be cautious.

This would be as opposed to a red flag and removing the data which generally is only used for a confirmed hard failure or a critical failure that threatens loss of control.

Of course I am an engineer but NOT a pilot so actual pilots may have a better method to make sure they are notified when they should not trust the AOA.

 

[azcats]

So the MAX has (2) AOA sensors standard?

And the AOA DISAGREE alert was intended to be enabled on all MAX planes but was not by some mistake?

Was there additional code that MCAS would not operate when there was also an AOA DISAGREE alert? If this were the case at least the design didn't intend to rely on one sensor.

 

[Alistair_Heaton]

If they got a mismatch on takeoff before v1 it would be a mandatory high speed rejection.... Blown tyres etc.

In air if they had known about the mcas system they could of turn off the electric trim problem solved.

 

[azcats]

Forgive the dumb question, but I thought the second plane knew about MCAS?

 

[LittleInch]

AoA disagree was an "extra" but now Boeing are trying to say it shouldn't have been.

~There was no code about AoA disagree, just a warning. The MCAS system worked with the FCC on whichever side was in action at the time ( either pilots or FO side, but only one AoA input into the MCAS.

The second plane seemingly knew about the issue and managed to disable the electric trim after the initial operation, but for reasons unknown didn't manage to trim the plane back to where it needed to be before disabling the electric trim and as it sped up things seemingly got worse and the plane was clearly not in stable flight.

As far as the evidence released to date shows it appears then then re-energized the electric trim to try to gain control, but then the MCAs kicked in again and at the high speed they were now travelling at they couldn't hold the dive ( after going negative G)



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

 

[waross]

The Max 8 was to be designed within management restrictions that may have prioritized profit and sales over good engineering.
Engineering by management decree is not always a good thing.
I experienced that at one company. Within a year after I had left, every designer who I respected had left.
The founders last words to the CEO were to the effect:
"I've had it with you, you SOB. Have your lawyer contact my lawyer and arrange to buy me out. I'm out of here."
How many tries and how many mistakes has Boeing had with MCAS?
How much have they saved?
Costs to Boeing are estimated at One Billion. This will probably go higher.
Costs to three Airlines are estimated at $600, Millions. (corrected, thebard3)
Total costs to all Airlines will be most likely be several Billions.
I expect that most of them will try to recoup these losses from Boeing.
And Boeing management is still in denial.
Every week there seems to be another MCAS issue surfacing.
Is this an example of the last stages of the Peter Principle?


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

 

[thebard3]

Costs to three Airlines are estimated at $600,000.

Did you forget some zeroes?

Brad Waybright

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

 

[3DDave]

To balance that, it appears that some airlines have also prioritized profits and cut corners on pilot training and that thousands of uneventful flight hours are not a substitute for learning how to manage an uncooperative plane that is still controllable.

In the total there are several billion decisions that went into building those planes and putting those pilots in those seats and only a couple were required to get MCAS where it was and a bunch more were required to get leave the pilots unable to cope.

Consider the accident chain that put the Indonesian flight into the ocean that included 3 pilots failing to inform anyone that they had to shut off the trim motors to shut off, for them, random trimming, not even mentioning that there was a third pilot who made that specific decision in the preliminary report. Putting a fundamentally crippled plane back into the air with another spin of Russian Roulette choice in pilots isn't Boeing's fault.

Boeing and the airlines share responsibility for this and Boeing engineers can ensure they are not the source of this problem again; the airlines, on the other hand, seem to have done nothing noteworthy to fix their contribution.

 

[SwinnyGG]

If I were involved in the design, ..... make sure they are notified when they should not trust the AOA.

Caution alerts in highly complex aircraft like this one follow a very regimented system. The AoA disagree state would cause a master caution, indicated by the separate master caution light on its own panel. This indicator tells the pilot several things, all at once:

1) there is something wrong
2) light state (color, etc) indicates the severity of the fault, there are multiple levels
3) Subsystem indicator (the shortened titles next to the caution light) indicate which major system is affected, which tells the pilot which diagnostic procedure to follow or which panel to look at for specific information

None of this stuff was seat-of-the-pants by Boeing. The AoA mismatch would be part of the main caution process flow just like airspeed mismatch would be, as long as the option is correctly activated in the software which they are now saying was not the case.

 

[RVAmeche]

Of course an airline would take a new plane w/ minimal training compared to a new plane with substantial training. That's not their fault it's their prerogative.

However, Boeing and their too close relationship with the FAA (or lack of oversight), meant that Boeing was inclined to ensure that a new plane needed minimal training. The fact that no one knew enough to call them out and not allow this, or didn't look at all, is the major issue IMO (potential design faults excluded).

 

[VEBill]

I've seen old fashioned 'steam gauges' on aircraft where a checkerboard curtain was drawn across the gauge (hiding the indicator) to not only clearly indicate system failure, but also inherently hide the bad indication.

 

[Alistair_Heaton]

The same happens on modern efis displays as well. If there is any doubt in the data it changes colour. Then you go on the standby instrument reconfigure things then it changes colour again to make sure you know that your in a degradation mode and you need to manually cross check with the standby instrument.

 

[3DDave]

The "closeness" with the FAA is not the source of this problem. It's that someone developed a convincing case that MCAS was a minor tweak to manage stick-feel; the sort of case that would have also been acceptable by anyone, including the airlines that bought the plane.

The failure seems to be one of imagination, much like what led to 9-11, where no one reasonable thought that hijackers would not need the pilots and that the planes would be used as cruise-missiles.

 

[waross]

I keep wondering how much maximum correction the lift from the engine trust and placement needed.
Is there a flying condition where the plane is not stalled, but full trim down is needed to counteract the engine lift effect?
If the plane was flyable with the maximum needed correction, it may have made sense to limit the authority of MCAS to needed correction rather than full trim down.
This could have been done in either software or hardware.

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

 

[itsmoked]

BIll; I believe as the plane climbs out the steeper the climb the more out of trim it gets, a classic feed-forward problem. The MCAS system designed to prevent a decaying feedforward AoA problem was throwing in 10 seconds of trim and then seeing that wasn't enough and throwing in more. Then more. The system thought the plane was climbing at a progressively steeper angle, as we now know a totally bogus problem unfortunately.

Keith Cress
kcress -

http://www.flaminsystems.com