Endless Argument
 

How can this discussion become any more wearisome (albeit fascinating at the same time) than it has? To a dispassionate bystander with a decent grasp of the technical AND human factors involved and NO axe to grind (such as myself :8 ) it has seemed obvious, pages ago, that there is plenty of blame to go around! No-one will emerge blameless from the analysis. All of the arguments from the various POVs here make sense, and only serve to show that almost everybody screwed up! 'Course if we all adopted that POV there'd be no discussion, and what fun would that be?

STAB TRIM switches. So, the two little switches on the pedestal look the same and feel the same as those on a 738 etc. But the little white labels say something different and do something different. This isn't indicated anywhere in flight manuals, checklists, training software/documentation etc? What else has changed but isn't covered in the 'training manual'?

Hmmmm. The more I look at this the more I think the MAX has been a third-rate job. Yep, clearly the crews got it wrong. :rolleyes:

I agree they shouldn't have done that. I didn't say it wasn't a mistake. I was just saying it wasn't a mistake that is hard to explain. There are maneuvers that force you to get to the edge of the envelope to save the aircraft, like the terrain escape maneuver. So, out of everything they did, this is probably part that is the easiest to explain and excuse.

However I disagree with the statement that they kept accelerating. They accelerated for the first 2 minutes but, after getting close to VMO, their speed remained almost constant for about 3 minutes. The airspeed traces on the FDR chart were almost flat. They were not accelerating until MCAS activated again and brought the nose down.

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.

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.

Indeed, I've personally seen no evidence of a successful outcome from this scenario other than for Lion Air #1

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.

Look like it's Boeing flight test. There is a placard below the FO's display that appears to read BOE 104 EXPERIMENTAL.

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.

See this post:

IIRC, subsequent discussion was inconclusive about any link between those events and the JT/ET accidents.

It's post #981, at present.

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.

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?

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.

> 5 KIAS for > 5 sec. If they didn't have this at rotation, they would have had it very shortly thereafter.

Yes, but procedurally incorrect. One of the first steps of UAS is to disconnect the A/P.

Only if one airspeed/AOA was registering low enough to trigger a stall signal from the Stall Management Yaw Damper (SMYD) computer.

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

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.

Takwxs, Appreciate the clarification.