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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 14th Apr 2019, 17:54
  #4001 (permalink)  
 
Join Date: Jul 2011
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Fly the damn airplane...

We can debate all day long about whether MCAS is a piece of crap, whether pilots should or should not have been given more information about it, etc., etc.
The overriding issue with both Lion Air and Ethiopean is why they could not manage the aircraft whereas, as it has been reported earlier in this thread (about 4,000 posts ago) that this same event happened at least five times with US carriers and they all managed to safely gain control of the aircraft and land safely.

The moment the aircraft lifted off in all of these situations they had an unreliable airspeed situation - disparity between airspeed indicators, the stick shaker active. The B737, like all airliners, have three independent altimeter, attitude indicators and airspeed indicators. A quick look at the other two or simply by asking the pilot not flying what his or her airspeed indicator says and comparing it to the standby would quickly isolate which one is unreliable. That is basic airmanship.

This is a textbook UAS event. It's a memory drill - flight directors off, autopilot off, auto throttle off, set an appropriate pitch/power setting for phase of flight. None of this was done. And, as I pointed out earlier, even if the Ethiopean crew thought it was a bona fide stall, you do not engage the autopilot. Period. Moreover, if the aircraft is indeed in a stall, why on earth would one raise a high lift device like the flaps and deepen the stall? Airmanship again. So even before the MCAS event, things were way off the rails.

When the flaps were up the MCAS activated. Having the nose pitch down without any manual input while manually flying the aircraft is a text book stab trim runaway. There is a memory checklist for that too which, among other things, calls for turning off the stab trim switches. And turning off the electrical stab trim kills any MCAS nose down trimming.

I know that it is harsh to criticize the pilots and all too often "pilot error" is the the go-to answer but these aircraft, as the US pilots demonstrated, were completely flyable if the crews simply did what they should have been trained to do yet not one of the memory drills was completed. Even if the airspeed unreliable drill was done and the power setting brought back from 94% to 80% while climbing then 75% when leveled off, the speed would have been such that manual hand wheel trim would have been possible even with MCAS active. This would have bought them lots of time to sort out the runaway trim despite not knowing the memory drill. As we know, the speed got way out-of-hand, past Vne, making manual trim with the hand wheel impossible.

I might be old school, but I believe that professional aviators are paid to know their stuff including knowing their emergency drills, particularly the ones that are memory items. They are memory items for a reason as the control of the aircraft is at stake as we have seen tragically demonstrated in these MAX accidents. Would we turn a blind eye to physicians not knowing how to do CPR? I think not nor should we shy away from criticizing pilots for not knowing two emergency drills designed to cope with situations just like this; hopefully the industry can learn from these accidents and put a lot of focus on pilot training and experience.
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Old 14th Apr 2019, 18:12
  #4002 (permalink)  
 
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Originally Posted by L39 Guy View Post
this same event happened at least five times with US carriers and they all managed to safely gain control of the aircraft and land safely.
Do we factualy know it was the same or just outwardly similar?

It would have to be an identical scenario for this to mean anything.


Thrust Augmentation is offline  
Old 14th Apr 2019, 18:15
  #4003 (permalink)  
 
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Originally Posted by Takwis View Post
Documentation, please...this is the first assertation of this that I have heard. Frankly, I don't think that it is true.
Indeed, I've personally seen no evidence of a successful outcome from this scenario other than for Lion Air #1

Originally Posted by L39 Guy
I might be old school, but I believe that professional aviators are paid to know their stuff including knowing their emergency drills, particularly the ones that are memory items.
I'm also old-school and I was taught to know the effect of every switch and system before I used it. It seems that the MAX manufacturer wasn't too efficient in giving us old-school pilots that sort of information.
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Old 14th Apr 2019, 18:20
  #4004 (permalink)  
 
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Originally Posted by Takwis View Post
Who has a GoPro camera mounted on the windshield, pointed at the F/O's seat?
Look like it's Boeing flight test. There is a placard below the FO's display that appears to read BOE 104 EXPERIMENTAL.
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Old 14th Apr 2019, 18:32
  #4005 (permalink)  
 
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Originally Posted by L39 Guy View Post
The moment the aircraft lifted off in all of these situations they had an unreliable airspeed situation - disparity between airspeed indicators, the stick shaker active.
...
This is a textbook UAS event. It's a memory drill - flight directors off, autopilot off, auto throttle off, set an appropriate pitch/power setting for phase of flight. None of this was done. And, as I pointed out earlier, even if the Ethiopean crew thought it was a bona fide stall, you do not engage the autopilot. Period. Moreover, if the aircraft is indeed in a stall, why on earth would one raise a high lift device like the flaps and deepen the stall? Airmanship again. So even before the MCAS event, things were way off the rails.
...
.
Not sure that we know for a fact that ET had a UAS warning. The (frustratingly limited) log in the ET prelim report reports that the displayed speeds diverged but no mention of UAS.
From the FDR plot the 2 speeds are not widely different at first although it is hard to read absolute values.

What is the trigger for UAS warning?

Can the autopilot be engaged while UAS warn is active?

Also puzzled by 'the stick shaker active' in above, is this an expected side effect of all UAS events?

I could well be missing something here so stand ready to be corrected/further enlightened.
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Old 14th Apr 2019, 18:43
  #4006 (permalink)  
 
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Originally Posted by Takwis View Post
Documentation, please...this is the first assertation of this that I have heard. Frankly, I don't think that it is true.
See this post:

Originally Posted by ManaAdaSystem View Post
So the Americans have had 5 cases of control issues after takeoff on the MAX. At least two happened when they engaged the auto pilot.
There appears to be several issue with the MAX.
IIRC, subsequent discussion was inconclusive about any link between those events and the JT/ET accidents.
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Old 14th Apr 2019, 19:00
  #4007 (permalink)  
 
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Originally Posted by Takwis View Post
So, at least two were autopilot related (and MCAS supposedly won't work with the autopilot on), and the others were "inconclusive". Just like the two fatal crashes...yeah.

Is there an easy way to find that exact post, from the information here? Not real competent at working this website, yet.
It's post #981, at present.
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Old 14th Apr 2019, 19:34
  #4008 (permalink)  
 
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Originally Posted by wonkazoo View Post
I've been mostly silent on this thread...

You 737 drivers out there: If you are clocking 320KIAS and you try to use the trim- will it work if you are somewhat mis-trimmed nose-down?? 300KIAS?? 310KIAS?? Where and when does your trim tab become teh hammer nailing the lid shut on your coffin?? I am stunned to see here that people are not discussing this more. MCAS is an abomination, but alone it is simple stupidity. An Airplane that has an envelope within the normal operating range wherein trim will no longer not only be detrimental, it will me immovable...Really??
Your break from cover is appreciated as there are too few of us posting on this thread with astonishment that the manual and electric trim performance envelop is not defined for the 737 NGs that are still out there flying today.

All we have is a statement from EASA noting that the electric trimmers don't work in part of the performance envelop, complete with a reply from Boeing to say it is 'feature' and that manual trim remains available throughout the envelope. Of course, we now know that Boeing's statement to EASA was a falsehood known to Boeing for decades. If Boeing had answered the question correctly then, just maybe, these accidents may never have occurred.

But that would have deprived so many from the opportunity to blame fellow pilots who really didn't want to die or experienced the pain, fear and anguish trapped in those final frantic moments.

RIP guys - many of us do respect the price you paid and hope that aviation does re-learn the terrible lessons of a corrupted certification process that put the manufacturer above the regulator.

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Old 14th Apr 2019, 19:44
  #4009 (permalink)  
 
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Originally Posted by Takwis View Post
Stabilizer trim was not mentioned in my MAX training at all. The labels, or functions, of the cutout switches were not mentioned or noticed.

I am re-watching all the videos, now, to make sure I didn't miss something.

Further Editing:
Aircraft Exterior: 8" longer nose strut, Bigger engines, gross weight limitations, tailskid, dual strobes on tailcone.
Flight Instruments and displays: 35 slides about the new, larger displays.
System Differences: HGS, Navigation, Anti-Ice, Air Conditioning, APU, Engines, FLIGHT CONTROLS, FBW (spoilers, speedbrakes, LAM, Ground Spoiler Control Module), fuel system, Landing Gear, Speedbrake light.

Of those the Flight Controls are the relevant section. Under Flight Controls are:
Slides of the new "Spoilers" malfunction light on the overhead panel, and the new Elevator Jam Landing Assist panel, with a light and a guarded switch.

Wrap up: Vertical Situation Display, N1 bugs, Engine Start, New Alert Lights.

That's it. NO MENTION OF ANY CHANGES TO TRIM, TRIM SWITCHES, TRIM SWITCH LABELS OR FUNCTIONS. Or MCAS.
Which means, pilots did not know about the revised trim cutout switches functionality on the MAX?

What does PRI and B/U mean? Would putting PRI to off and B/U on leave MCAS engaged?

Coming from the NG the F/O may have tried to switch off autopilot stab trim only, leaving electrical manual trim to counter MCAS?
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Old 14th Apr 2019, 19:52
  #4010 (permalink)  
 
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Undisclosed changes in switch function

1 As I gather, on previous versions one cutoff switch blocked autopilot trim while allowing electric trim to continue working. The other switch cut off power to the trim motor from all sources. With the advent of the MAX, you now have to give up electric trim to block MCAS.

We do not yet know how effective electric trim is when the stick shaker is operating. Possibly the usual light touch on the switch may not be enough to sustain electric contact with stick shaker on. Have to wait for the report on that unless somebody finds time to research it on a sim.

2 The underfloor control column switch blocks autopilot trim, but not MCAS

Neither seems to have been disclosed.

We can talk about crew training, but the new MAX curriculum seems short on vital facts.
RatherBeFlying is offline  
Old 14th Apr 2019, 19:57
  #4011 (permalink)  
 
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Originally Posted by MurphyWasRight View Post
What is the trigger for UAS warning?
> 5 KIAS for > 5 sec. If they didn't have this at rotation, they would have had it very shortly thereafter.

Can the autopilot be engaged while UAS warn is active?
Yes, but procedurally incorrect. One of the first steps of UAS is to disconnect the A/P.

Also puzzled by 'the stick shaker active' in above, is this an expected side effect of all UAS events?
Only if one airspeed/AOA was registering low enough to trigger a stall signal from the Stall Management Yaw Damper (SMYD) computer.
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Old 14th Apr 2019, 20:07
  #4012 (permalink)  
 
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Originally Posted by safetypee View Post
VicMel, thanks,
With that info and previous analysis, how might the correction routine ‘reset’, if it did, between flights?
How or why would this corruption occur on the particular accident flights apparently at random, or reoccur after the first Lion incident; conversely why were there not more instances of inaccurate AoA.
Before I address your specific points, I’ve had a re-think on some aspects:-
1) I had noticed on ET302’s FDR that the pilot, just after take-off, seemed to stop pulling the Control Column back a few seconds before the Stick Shaker started! I had suggested that perhaps it was just a latency due to ARINC 429 different data rates; however, I cannot find the same effect on the 2 Lion Air FDRs, so I now think I was wrong. Instead, I think it is plausible that the pilot realised that the nose was coming up too quickly and so backed off. When the Stick Shaker kicked in he could have thought it was due to his over-enthusiastic take-off (perhaps because of shortish runway and heavy load) and that a real stall was threatened. The idea that it was an ‘AoA Disagree’ would not occur to him, it might have taken several vital seconds later, after working to resolve a problem that did not exist, before the crew realised that something other than the pilot’s action was the problem. We know Boeing introduced MCAS because the new MAX engines, being more powerful and lower slung, together with the effect of a larger cowling, would have a larger coupling moment. So without MCAS cutting in, a significantly larger Pitch Rate than on a 737NG is fairly easy to achieve.

2) The larger Pitch Rate might be significant because the AoA Pitch Rate correction software would have had to be modified because the big new engine would have had an effect on Wing AoA. The original software in the ADIRU would have been written several decades ago and now someone who is unfamiliar with it is going to patch that software, they are told the software is not safety critical, and it is a rush job! Recipe for a huge hole in the cheese!

3) The software in the ADIRU has to deal differently with L AoA than with R AoA. There is a sign difference as a positive increase in real world AoA will result in a clockwise motion of the L AoA sensor shaft, but anticlockwise on the R one. Fairly obviously, the Sideslip correction has to be different for L & R AoA sensors.

4) Considering how long ago it was written, I suspect that the original software used fixed point calculations, in which case the original scaling for Pitch Rate may well not be sufficient to cope with the new larger value and so an overflow will occur. I doubt that the person who wrote the patch would be aware of such subtleties.

5) Overflows in software are a bit unpredictable, it all depends what action the hardware and software take when one is detected. The result could be a smallish offset, say 22 deg on AoA, with any lower level noise retained. It could be huge, say 1000 deg, in which case AoA could be any value from 0 to 360, and as a flat line. Any sudden large value could take several seconds to be smoothed out.

So, to go back to your original queries,:-
How might the routines reset? A restart of the computers would do that, just like with Windows.
How would the corruption occur on particular flights? Any flight with a high Pitch Rate could be a trigger. Or anything that has been patched for MAX could be a problem, patched software is notorious as a source of failure. Far more likely than a failure of a piece of hardware that has proved in-service to be very reliable.
Why not more instances? Good question, perhaps in the developed world we have fewer shortish runways and “high and hot conditions”, which according to Boeing, MAX is not suited to.

Vic
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Old 14th Apr 2019, 20:27
  #4013 (permalink)  
 
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Fly the Aircraft....

Once again, pitch, power, performance.

It really doesn't matter how many bells, whistles, lights, or whatnots were going off at rotation. When the proverbial $hit hits the proverbial fan - pitch, power, performance. If the PIC of a commercial airliner can't look at those three items and determine whether or not his/her aircraft is performing anywhere near expected parameters within 30 seconds of rotation, then he/she should not be in that seat. Tough words, but I'm sorry, that's why we have that ATP ticket.

Then.... Confirm.

Again, it doesn't matter what instrument, light, bell, or warning is trying to grab 100% of your attention, you need to fly your aircraft and then confirm any warning by whatever means you have at your disposal. By around 500-1000' off the ground, this crew should have been narrowing in on the nature of the problem and formulating their response - not trying to engage the automation.

Yes, Boeing screwed up the MCAS design. Yes, the crew could have worked the UAS problem correctly and still had the MCAS try to kill them later. In that case, the answer would still be the same - fly the aircraft. First, last, and always.

Every time a pilot takes to the air, someone could have screwed up something and left us with a malfunctioning aircraft. That malfunction may or may not follow some preconceived notion we have about how our aircraft or systems should respond. It is at that moment that it is critical to fall back to the basics - pitch, power, performance. Stabilize the aircraft, get to a safe altitude, and then try to identify the problem.

This crew did not do that. Period.

Why they did not do that should be a significant focus of the investigation.
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Old 14th Apr 2019, 21:32
  #4014 (permalink)  
 
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Close, RBF. In the NG, the left one is labeled "MAIN ELECT" and the right one is "AUTO PILOT". MAIN ELECT "deactivates stabilizer trim switch operation" and AUTO PILOT "deactivates autopilot stabilizer trim operation". A few pages later, "The STAB TRIM MAIN ELECT cutout switch and the STAB TRIM AUTOPILOT cutout switch, located on the control stand, are provided to allow the autopilot or [my emphasis] main electric trim inputs to be disconnected from the stabilizer trim motor." They are wired in parallel.
Takwxs, Appreciate the clarification.
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Old 14th Apr 2019, 21:33
  #4015 (permalink)  
 
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VicMel, #4055, thanks very much for the detailed clarification.
Your views appear to strengthen the software argument, and in answering my questions clarifies the possibilities for local variation. But why just before takeoff (taxying bump, elect transient/switching) / just after take off; pitch rate again?

Stretching the hypothesis a bit more - higher takeoff pitch rate, hot / high operations, takeoff config / speeds, (takeoff pitch attitude limiting ?); also we might consider differences in training or in operating previous versions of the 737. Another pitfall of same type rating, minimum training requirement, no simulation?
Would a simulator (training or design) ever reproduce this type of software error ?
Opportunities for some alternative sleuthing.

Last edited by safetypee; 14th Apr 2019 at 21:44.
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Old 14th Apr 2019, 21:47
  #4016 (permalink)  
 
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Originally Posted by Takwis View Post
Who has a GoPro camera mounted on the windshield, pointed at the F/O's seat?
Suspicious F/O's spouse?
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Old 14th Apr 2019, 22:06
  #4017 (permalink)  
 
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Originally Posted by Takwis View Post
Another questionable statement. For almost three minutes, the speed was nearly constant, right at VMO. The autothrottles were still engaged. The trim "didn't work"...whatever that may ultimately mean. But the aircraft did not overspeed until the final MCAS input sent it into a deep dive.
Accordind to the FDR data in the preliminary report, around 05:41:20 the aircraft exceeded Vmo according to the right side (correct) airspeed. This is well before the dive or the final MCAS input.
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Old 14th Apr 2019, 22:16
  #4018 (permalink)  
 
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Originally Posted by Just This Once... View Post
All we have is a statement from EASA noting that the electric trimmers don't work in part of the performance envelop, complete with a reply from Boeing to say it is 'feature' and that manual trim remains available throughout the envelope. Of course, we now know that Boeing's statement to EASA was a falsehood known to Boeing for decades. If Boeing had answered the question correctly then, just maybe, these accidents may never have occurred.
As previously discussed, the manual electric trim does not have the capability to trim to the "full limit" of the stab. This is claimed as a "safety benefit" to prevent unintentional mis-trimming.

MCAS, and the manual trim wheels, do have the ability to move the stab all the way to its mechanical limit. The manual electric trim can be used to move the stab in the opposite direction if it has been manually cranked (or moved by MCAS, or runaway, etc) past the aforementioned limit.



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Old 14th Apr 2019, 22:44
  #4019 (permalink)  
 
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Originally Posted by ams6110 View Post
(Not a pilot). It crossed my mind, would it not be customary in a "stick shaker" situation for the FO/PM to call out that it was one-sided and his instruments were still normal? Maybe because the FO had such low hours he would not have recognized or felt confident pointing this out? Or is it not immediately obvious?
OF COURSE IT IS! THAT'S THE WHOLE POINT!
Had they done this and followed up CORRECTLY with the blindingly obviously necessary UNRELIABLE AIRSPEED checklist this whole disaster would almost certainly not have happened.
meleagertoo is offline  
Old 14th Apr 2019, 23:35
  #4020 (permalink)  
 
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Stall warning and overspeed warning. Why are they there? It is 2019. You have at least 3 ASI's. You don't need a sledgehammer or a siren to tell you when something is wrong. You can see in silence from various displays where the problem is. A master caution light that you can reset should be enough.
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