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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 5th Apr 2019, 13:59
  #3321 (permalink)  
 
Join Date: Jan 2019
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Originally Posted by JesusonAHarley View Post
I usually don't contribute anything to a discussion, preferring to listen more to what everyone has to say. This is reflected in my posts on here too, which are non-existent. However, I have been following this thread very keenly and am very grateful to all the amazing insights and points of view provided. I'm a NG/Max driver and coincidentally, flew a Max on both the crash days.

Generally, my attitude towards any incident / accident is "They should have done this. But, I wasn't in that hot seat. Maybe I would've done the same". However, I've been struggling a lot trying to get that attitude and the posts on here have helped. Especially the ones which have been downright condescending of the operating crew. They have helped me get my perspective.

One thing that I have noticed in the preliminary report of the ET is that the pilot ANU stopped at exactly 2.3 units on three separate occasions. The first one was a shallow pick-up after the first MCAS activation. The second one was a more agressive pick-up immediately following the second MCAS activation, suggesting that the pilot(s) now knew what they were dealing with. As soon as the ANU stopped at 2.3 units, FO asked if he should cut-off the stab trim. The third was when they, presumably, reactivated the stab-trim to get some leverage with the electric trim and ended up with short bursts, instead of a long ANU activation.

With discounts given to adrenalin not allowing you to feel the AND for the first one and coincidence being the second, the third ANU also stopping at 2.3, suggests there was something else at play and not merely pilots not knowing how much to trim. The clue is provided in the timing of the FO suggestion for stab-trim cut-off.

Or am I reading too much?
I understand where you are coming from. I, too, was appalled at the attitude of some on here- stating the pilots must have been wrong based on where they came from. I also hypothesised a very similar scenario on 13th March- post 1171- all that I hadn't mentioned was the difficulty in turning the trim wheel at higher speeds, but I'd assumed that would be obvious if anyone looked at the indicated airspeed from the ADS-B data that was available at the time! (Put your hand out the window of your car when you're driving at 60mph/100kmh- it's a lot easier to move back and forward than at 100mph/160kmh!) The roller coaster movement I had never heard of before- and not sure if this would have been an option on this flight given the speeds and altitudes involved.

Mentour pilot's video was fantastic, it was uploaded prior to the publication of the preliminary report, it's a shame he has removed it. He also stated the reason for doing the test was because too many people instantly blamed the pilots just because of the geographic location of where they worked!

I also have a couple of queries about the data:

All the electric trim inputs from the pilot are short throughout apart from one...:

At 05:40:27 the Captain advised the First-Officer to trim up with him.
On this occasion, the trim moved 1.9 units ANU over a period of 8 or 9 seconds! This is the only occasion in the entire flight where the pilots were able to command ANU trim for any longer than 2-3 seconds. Possibly your point and my point are related to the 2.3 unit mark. Otherwise, is there some reason that the Captain's trim switches were compromised? It is the only time in the transcript where the Captain requested the FO to trim up with him. With the Captain's stick-shaker activated etc. would this possibly cause any complication to his trim commands being tripped out so soon each time? Is there another hidden 'safety' system that limits the pilot trimming up when stick-shaker is activated? Or is it simply just a case of the motor not being able to operate due to the increased forces at the given airspeed (when considering the blips later on)?






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Old 5th Apr 2019, 14:02
  #3322 (permalink)  
 
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Originally Posted by fdr View Post
BSU,

Before the big bang there is no experience, after the big bang there is experience. The individual chance of a critical system event occurring is unassociated with experience. The risk of a bird strike, engine failure, trim runaway is equally distributed across the career of the crew member. The recovery method suggested by the FCTM is apparently problematic given recent history, and the wording is hardly confidence inspiring. If the pilot was old enough to have had training that included the gems on this that are coming out now, then that is wonderful, and all would still be right in the world. Reading the FCTM alone would not necessarily result in competency in conducting the implied manoeuvre, one which assumes that there are two pilots in the seat at the time, and that sufficient altitude exists to recover the aircraft from the trim problem.

The more reflection on the recovery technique, the less it appears to be reasonable to be conducted, and at the very least the more necessity there is to undertake the training in the simulator. A yo-yo manoeuvre is not what one expects to be needed in a Part 25 transport, it is likely to spill the champagne in the front and to end up with a flight attendant shaped dent in the overhead lining down the back. The calendar indicates this is now 2019, and the FCTM suggests in rather vague terms a procedure that is essentially aerobatic, and Wilbur and Orville would have not been so happy with in 1903.

The design standard and the design is unlikely to be changed any time soon, but anyone considering that the crew of these two accidents were deficient in dealing with the trim condition needs to take a look in the mirror, and think seriously about the situation they were placed into. Post hoc, it is quite easy to say "I woudn't have done that" or "I would have done this", but I can say that I trained late in my jet career on the 73, under an FAA 142, and the implied procedure of the FCTM was not a takeaway, conceptually or in practice. Having flown some rather lousy designs where jack stall could occur, the concept in the unloading is not alien, but when the procedure calls for both pilots on the controls at the same time, and to undertake a ballistic flight path either upwards or downwards as determined by the in trim speed that has been established by the uncommanded motion, that just doesn't appear to gel with the spirit of RPT jet transport certification by the leaders of the worlds aerospace regulators.

The recovery technique that is implied in the FCTM, and which is not incorporated in the QRH as a recall item, is rather depressing, no matter how much lipstick is put on it.

In respect to the "errors" suggested to have occurred, the alternative observation is the pilot had ascertained that the stall warning was spurious, and therefore engaged the A/P, and retracted flaps. Perhaps he had a compelling reason to maintain speed, perhaps arising from the fact that the AOA outputs to the ADIRU and alters that sides IAS as a function of the sensed AOA, a refinement of the air data system... therefore having both AOA and IAS issues, the pilot elected to prudently maintain power to gain separation from the hard stuff. Perhaps. Equally as likely, under the assault of information and task demands that confronted the pilots, they were cognitively overloaded. Perhaps. Getting into a situation where you are leaving teeth marks on the elevators is never fun, and even less when there is a risk of catastrophic outcomes. The next crew to experience such conditions will have been gifted the insight that sober reflection on the situation that befell these crews. Whether the pilot had 1.5 years or 150 years is unlikely to be a factor in the outcome of the event, IMHO.
This sums it up nicely as far as I can judge. No matter the outcome of the investigation, the mere suggestion of the above scenario should send shivers through everyone's spine.

Regarding the thrust, whatever the reason they were still producing 94% thrust, may I add the sobering thought that reducing the thrust would have lowered the nose even further...
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Old 5th Apr 2019, 14:02
  #3323 (permalink)  
 
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Besides having made time during the 6+ minutes of flight to navigate (setting and resetting altitudes/headings) and to communicate multiple times with ATC, it's hard to conceptualize how at low altitude in day VMC neither pilot had reacted to the obvious increasing cockpit noise from the rush of a air in the slipstream as the jet zoomed to 458 kts IAS and beyond clacker speed to 500 kts. The 29 year old captain's purported 8000 hours' experience level obviously lacked depth in situational awareness and manual control of the thrust levers.
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Old 5th Apr 2019, 14:14
  #3324 (permalink)  
 
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I am just a glider guy and frequent SLF, I am very surprised every time I read about the low number number of hours in these posts. My clubs insurance wanted to me to have 500 hours total time plus 250 hours tail wheel to fly a clapped out agwagon dragging gliders around. Do insurance companies not set standards in the airline world?
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Old 5th Apr 2019, 14:45
  #3325 (permalink)  
 
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Originally Posted by Luc Lion View Post
Sorry, confirmation bias ; I positively checked that it wasn't the flaps and then I misread another line for being the gear (was probably the AP).
So something was retracted, but it wasn't the flaps and probably not the gear.
Autopilot engages, gear must be up for that to happen, no?
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Old 5th Apr 2019, 14:45
  #3326 (permalink)  
 
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Originally Posted by positiverate20 View Post
With the Captain's stick-shaker activated etc. would this possibly cause any complication to his trim commands being tripped out so soon each time? Is there another hidden 'safety' system that limits the pilot trimming up when stick-shaker is activated? Or is it simply just a case of the motor not being able to operate due to the increased forces at the given airspeed (when considering the blips later on)?
Would the trim motor not be able to move the stab, we would still see the trim command from the pilot.

The same when trim cutout switches were off, we don't see any change in stab position but we still see MCAS AND command
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Old 5th Apr 2019, 15:06
  #3327 (permalink)  
 
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Originally Posted by jimjim1
I offer an explanation for the behaviour of the Left hand AoA indication throughout the flight.

If the vane had been lost the AoA sensor would become unbalanced about its usual axis or rotation. The internal balance weight** would then cause the axle to be subject to movement when the aircraft transitioned from +g to -g. +g would cause the indication of +AoA. (If I have got this the right way round
Originally Posted by MurphyWasRight View Post
Excellent post, the tracking is almost too perfect to be believed at first.

This fits with the AoA heater fault as well, whatever happened caused 2 symptoms that are hard to explain except as physical damage to the sensor since the heater supply is independent of the resolver.

Someone commented that the pilots would have heard a bird strike, given the lack of a full CVR transcript we don't know if anything was audible.
I would suspect that the press conference statement of 'no foreign object' would suggest but not prove none was audible.

Anyone know if a departing vane by itself would cause a heater open?

One other observation is that the flight deck actions seem to be mostly normal until the AP disconnect, almost as though the stick shaker was activated but not working or noticed.
If missing from CVR that probably would have been noted.
Yes, a broken (losing its "winglet" part) or departing vane would explain AoA vs. gees curve and AoA heater fault.

If not a bird strike, it could be a previous damage which would have almost broken the vane. The AoA disagree happens when vertical acceleration is at its maximum (1,5 g or so) at the rotation. This acceleration would have finished to break the vane...
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Old 5th Apr 2019, 15:17
  #3328 (permalink)  
 
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Yo Yo

The idea of offloading the stab by releasing elevator input began when jet upsets began to be better understood.
At the very high speeds reached, the stab could not be trimmed while max elevator input was being applied. I believe it was a group including Boeing and Airbus who issued the advice (no particular aircraft in focus) to release elevator pull and trim (gently) the stab before applying elevator input again.
Of course in the case of an upset the procedure was not expected to be applied at treetop height but further up.
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Old 5th Apr 2019, 15:17
  #3329 (permalink)  
 
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Quick summary of events - please amend as necessary.
.

1. On take off, one of the AoA vanes is damaged.

2. 2 seconds after take off, stick shaker activates, resulting in understandable nose down pitch to gain speed.

3. Speed trim gives nose down trim inputs, as is usual - so trimmer is automatically trimming, as usual.

3. After flaps up MCAS becomes active, and gives large trim down - like a super speed-trim system.
... Pilots may think this is normal speed-trimming.
... (MCAS is using data from one sensor, which it should not be able to do.)

4. While sorting out the perceived stall situation, MCAS give two huge trim forward commands, half of which is wound back.
... (ending in a trim of 2.5 units, which is about 2.5 units more forward than usual)

5. Pilots are struggling with control, and turn off stab trim system. Some 50kg of force is needed to keep nose up.

6. If an attempt to engage autopilot was made it would be unsuccessful, as it cannot be engaged with stick pressure applied.

7. It is likely that manual trimming was attempted. But the manual trimmer will not work at these speeds and trim settings
... (the trimmer is jammed at 2.5 units, with full back elevator pressure applied.)

8. It is decided to reengage the electric trim system, so they can re-trim.

9. Trim system is reengaged, and two small trim-backs are made, to solve the out of trim situation.

10. But MCAS gives another huge dose of forward trim, wrenching the control column out of their hands, and pinning them to the roof.
... (it gives negative 0.5 g).

11. Control column is pulled full back, but cannot control the pitch, which continues to lower to -40 degrees.

12. Aircraft impacts ground.

.
Having tried this in the sim, I am surprised that full back pressure on the control column gave no response in pitch attitude. The sim did give a slow but positive response, although it took both pilots with maximum force to get a response and that response would be too slow in most circumstances. But on the real airplane, it looks like a stab-trim position of 1 unit at high speed renders the aircraft completely uncontrollable, and a crash inevitable. (They would understand that electric trim was faulty, and manual trim is not available at these trim settings.)

Silver

Edit: This was an NG sim, not a Max sim.....



Last edited by silverstrata; 5th Apr 2019 at 17:24.
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Old 5th Apr 2019, 15:33
  #3330 (permalink)  
 
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Originally Posted by silverstrata View Post
Quick summary of events - please amend as necessary.

1. On take off, one of the AoA vanes is damaged.
2. 2 seconds after take off, stick shaker activates, resulting in understandable nose down pitch to gain speed.
3. Speed trim gives nose down trim inputs, as is usual - so trimmer is automatically trimming, as usual.
3. After flaps up MCAS becomes active, and gives large trim down - like a super speed-trim system.
Pilots may think this is normal speed-trimming.
(MCAS is using data from one sensor, which it should not be able to do.)
4. While sorting out the perceived stall situation, MCAS give two huge trim forward commands, half of which is wound back
(ending in a trim of 2.5 units, which is about 2.5 units more forward than usual)
5. Pilots are struggling with control, and turn off stab trim system. Some 50kg of force is needed to keep nose up.
6. If an attempt to engage autopilot was made it would be unsuccessful, as it cannot be engaged with stick pressure applied.
7. It is likely that manual trimming was attempted. But the manual trimmer will not work at these speeds and trim settings
(the trimmer is jammed at 2.5 units, with full back elevator pressure applied.)
8. It is decided to reengage the electric trim system, so they can re-trim.
9. Trim system is reengaged, and two small trim-backs are made, to solve the out of trim situation.
10. But MCAS gives another huge dose of forward trim, wrenching the control column out of their hands, and pinning them to the roof.
(it gives negative 0.5 g).
11. Control column is pulled full back, but cannot control the pitch, which continues to lower to -40 degrees.
12. Aircraft impacts ground.

Having tried this in the sim, I am surprised that full back pressure on the control column gave no response in pitch attitude. The sim did give a slow but positive response, although it took both pilots with maximum force to get a response and that response would be too slow in most circumstances. But on the real airplane, it looks like a stab-trim position of 1 unit at high speed renders the aircraft completely uncontrollable, and a crash inevitable. (They would understand that electric trim was faulty, and manual trim is not available at these trim settings.)

Silver
Maybe the sim isn't programmed with the elevator blow back effect?
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Old 5th Apr 2019, 15:41
  #3331 (permalink)  
 
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Originally Posted by Luc Lion View Post
It was a great idea to have 2 cutout switches (up to the B737 NG) ; one acting on the yoke trim switches and the other acting on the autopilot and STS.
It was a not so great idea to replace them with a primary cutout switch and a backup cutout switch, both switches acting on both electrical channels of the trim.
This^^^ (my emphasis). If the actual change to the trim switches didn't threaten the manufacturer's certification strategy, I wouldn't expect that doing the sane and sensible thing -- disabling HAL's electric trim authority (STS, AP and MCAS, together or separately) while leaving the pilots' alone -- would be a problem. So, why . . .?

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Old 5th Apr 2019, 15:47
  #3332 (permalink)  
 
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Question Why

Originally Posted by JesusonAHarley View Post
I usually don't contribute anything to a discussion, preferring to listen more to what everyone has to say. This is reflected in my posts on here too, which are non-existent. However, I have been following this thread very keenly and am very grateful to all the amazing insights and points of view provided. I'm a NG/Max driver and coincidentally, flew a Max on both the crash days.

Generally, my attitude towards any incident / accident is "They should have done this. But, I wasn't in that hot seat. Maybe I would've done the same". However, I've been struggling a lot trying to get that attitude and the posts on here have helped. Especially the ones which have been downright condescending of the operating crew. They have helped me get my perspective.

One thing that I have noticed in the preliminary report of the ET is that the pilot ANU stopped at exactly 2.3 units on three separate occasions. The first one was a shallow pick-up after the first MCAS activation. The second one was a more agressive pick-up immediately following the second MCAS activation, suggesting that the pilot(s) now knew what they were dealing with. As soon as the ANU stopped at 2.3 units, FO asked if he should cut-off the stab trim. The third was when they, presumably, reactivated the stab-trim to get some leverage with the electric trim and ended up with short bursts, instead of a long ANU activation.

With discounts given to adrenalin not allowing you to feel the AND for the first one and coincidence being the second, the third ANU also stopping at 2.3, suggests there was something else at play and not merely pilots not knowing how much to trim. The clue is provided in the timing of the FO suggestion for stab-trim cut-off.

Or am I reading too much?
This!

Why did they never really reastablished an „in trim condition“ using electric trim early in the flight?

Why did they not use longer trim bursts to counteract MCAS before engaging the cutout switches?

Why did they not trim up after disengaging the cutout switches?

Its really hard to believe they pullend the controll collum back about 2/3 from nutral with massive force the whole time without ever trying to consequently using stab trim to get back into an in trim condition....
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Old 5th Apr 2019, 15:54
  #3333 (permalink)  
 
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bisieker #3350, Ethiopian airliner down in Africa

Bernd,
’ … had always assumed that in all but extreme out-of-trim situations, mechanical trim would be available.’

This is a very important point as it appears that the same assumption was in the EASA - Boeing case for equivalent safety as a means of compliance.
Boeing applied for a regulatory dispensation for the inability of the electric trim to achieve a trimmed condition throughout the aircraft’s speed envelope. Although this was unusual, but of importance that it was not described as a failure case, the use of manual trim was an acceptable alternative with caveats of training and normal procedure (not made available for 737 MAX ?).
Thus in normal operation, at all speeds, it should be possible keep the aircraft in trim, and able to correct small deviations (accel / deceleration), with the use of the manual trim wheel.

However, the abnormal situation where the aircraft is grossly out of trim (trim runaway) appears not to have been considered - or assumed to be the same as normal operation. This appears to be incorrect.
The difference in air-loads on the horizontal tail and elevator (https://www.satcom.guru/2019/04/stab...and-range.html) result in the inability of the trim wheel to overcome the forces and regain a trimmed state.

This situation was not posed in Boeing’s application, or it was assumed that FAA - EASA would consider it, possibly on the basis of similar approvals in NG (my assumption). Thus for trim runaways, the dispensation is insufficient to meet the regulatory requirements, but more important that there loss of all pitch control, trim and elevator effectiveness!

Either this represents a significant difference between the NG and MAX in the aerodynamics affecting the failure cases (likely), or that the NG is similarly non compliant in the failure case.
This could also question if Boeing actually tested the dispensation for the MAX in normal flight conditions - opposed to grandfathering it from the NG.
Also, to check that the abnormal NG procedures would still be effective in the MAX, again because of different aerodynamics (and apparently, without including the necessary procedures for recovery of a trimmed condition in the MAX manuals; the ‘roller coaster’ could not be flown).

These assumptions could leave some very big holes in the 737 MAX certification, not only being non compliant, but also un-flyable with some trim failures - where MCAS modification might only address one of them.

Last edited by safetypee; 5th Apr 2019 at 16:21.
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Old 5th Apr 2019, 16:17
  #3334 (permalink)  
 
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Originally Posted by Takwis View Post
Seems PERFECTLY reasonable, to me. They have expected US to do that (with passengers) ... they should first show us how it is done. (without passengers, of course)
Well, agreed, even though, as a passenger, I still would prefer that rollercoaster over hitting the ground with 500 mph. I those are the two choices left to us.
Maybe a new cabin announcement is in order: "In the unlikely event of a stab trim malfunction, the pilots will try to correct it with sudden rollercoaster movements. Please hold on to your dentures and glass eyes, and then help other passengers to not hit the ceiling."
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Old 5th Apr 2019, 16:28
  #3335 (permalink)  
 
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Originally Posted by Interflug View Post
Well, agreed, even though, as a passenger, I still would prefer that rollercoaster over hitting the ground with 500 mph. I those are the two choices left to us.
Maybe a new cabin announcement is in order: "In the unlikely event of a stab trim malfunction, the pilots will try to correct it with sudden rollercoaster movements. Please hold on to your dentures and glass eyes, and then help other passengers to not hit the ceiling."
Rolling the airplane on its back may be an interesting variation.
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Old 5th Apr 2019, 16:33
  #3336 (permalink)  
 
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I'm still struggling with the though that a grossly mis-trimmed stab on an NG cannot be recovered by either electric trim or by the strength of 1 or even 2 pilots cranking the wheels when the aircraft is at certain parts of the flight envelope.

As covered by others above, it seems bizarre to rely on having the airspace and time available to perform an acceleration or deceleration to a trimmable speed and/or perform a manoeuvre in the opposite sense to what you are trying to achieve in order to put the stab in a safe position.

Hopefully Boeing can enlighten us as to which parts of the performance envelop allow for PF solo cranking, PM dedicated cranking, both pilots cranking or just plain impossible to crank the wheel due to aerodynamic load. The NG is still flying and I am sure the AOCs would like to know, even if the FAA is asleep at the wheel at a benign 1G.
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Old 5th Apr 2019, 16:40
  #3337 (permalink)  
 
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Stab Trim Cutout on Stick Shaker in MAX?

At initial stick shaker, the aircraft can be expected to be in trim or not far from it. Better to head off MCAS at the pass than let it compound an already difficult situation to one where recovery is uncertain.

Electric Trim Availability?

It's been pointed out that the range allowed for electric trim is less than can be obtained from the trim wheel (airload permitting).

Does that mean electric trim can not be used to return trim outside its range back to within its range?
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Old 5th Apr 2019, 16:49
  #3338 (permalink)  
 
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Originally Posted by ecto1 View Post
I think there is a reasonable consensus (lest's say 50% chances) that vane shaft broke, keeping AOA vane attached or not, and subsequent alarms and checklists (both useful and useless) threw the crew out of balance. They didn't manage airspeed and lost ability to trim. They reengaged electric trim, was not strong enough either, forgot to CUTOUT, mcas trimmed down, EOF.

I think one of the biggest problems here is the compounding of stupidities. Each stupidity on its own is very much survivable, but all of them is a huge mess.

0. Of course MCAS MUST NOT BE operative with AOA disagree. Minimal software mod.

1. one AOA clearly fails, why not use a switch to transfer everything to the other (manually or automatically). It's a 3 way switch (AOA input L/NORM/R). In the event of stick shaker on, AOA disagree, check if any AOA is stupid (75 is quite stupid), switch to the other side, no more alarms in the cabin, crisis over in 10s tops. minimal wiring loom mod.

Even if you don't do it:

2. We have now perfect data about the influence of AOA over airspeed. 30 knots tops over the full AOA range and airspeed. Probably 15 knots 0 to 15 degrees 0 to 300 knts, probably less than 5 knots in the really tricky areas (slow). Upon AOA disagree, both airspeeds should use a default AOA value (4 deg maybe) instead of throwing UAS. and offer a reading with a possible +-7 knot deviation. But keep autothrottle and autopilot, maybe a caution message (airspeed calculation inacurate, stay 20 knots away from limits). Not a really disturbing unreliable airspeed, just because of a few knots. Minimal software mod.

3. Same with altitude. (altitude calculation inaccurate, stay 1000 feet clear from limits). Minimal software mod.

So that the only remaining alarm would be a stick shaker plus AOA disagree, and you still have autopilots. Much, much easier to handle. But if this is still enough for you to have the aircraft out of trim and miss speed management,

4. If speed goes over 280, message: reduce speed to regain trim ability). Minimal software mod.

My point is: most probably ANY of those mods would have saved the day, and all of them are pretty evident.

To me the problem is simply a huge lack of effort at design level to 1) Imagine 2) prepare for failures.


Chances are that the very same secuence of events, without MCAS final strike, has happened more than once before in other 737 variants (AOA fails, unreliable air data, stick shaker, big confusion, lack of proper aviation and or navigation and possibly all the way to overspeed and uneffective trim). Only without MCAS the aircraft would have been more or less in trim and therefore not nosediving and making the news.
Completely agree, great post, I have been thinkig along the same lines since the first crash, this one only reinforces that.

0) I think Boeing is working on that belatedly.

1). I flew the F50, and you could silence all/most alarms with a dedicated switch on one panel. I have read several accident reports that made me wonder if the crew would have done better without distracting and conflicting (stick shaker and over-speed simultaneously on Aeroperu flight PL603) error messages. Having a switch to deselect a system that gives an erroneous indication is an established concept in certifying aircraft (, and I think it should be a mandatory re-fit to all B737). Having one stick shaker go of on the failed AOA side with no other way to switch it off than going through the CB-panel isn't good enough.

2) + 3) Seems sensible, there might be areas in the envelope where this wouldn't work, so I can't positively endorse without more info.

4) Yes, UAS/AOA failure, max speed should be kept lower, so advise the pilots to lower their speed by reducing power is good, however, just lowering the limit so the clacker goes of brings me back to item 1)


Definitely Boeing needs to:
-Limit MCAS authority, and preferably by adding aerodynamic fixes like tail strakes.
-Disable MCAS in the case of AOA disagree.
-Install the AOA indicator and AOA-disagree indicator, preferably better than the current way.
-Install an AOA left/norm/right switch that limits error messages/stall warnings for those cases where it is clear to the crew which one is wrong.
-Bring back the option to disable auto trim (AP, STS ,MCAS, LAM), without losing the thumb-trim.
-Improve the NNC, to differentiate between MCAS and "regular" runaway trim.
-Verify it is possible to trim the aircraft back to in-trim from a runaway trim, aircraft full AND situation at low altitude, and see if there is any speed restrictions required for this, for all B737.
Obviously al of this should be paid by Boeing.

Maybe not all are required, but at this point I think Boeing better go the extra mile to make sure this doesn't happen again.

Also I do believe there should be more required training for pilots and more push in the SOPs to manually handle the aircraft, so people will not try to switch on the AP to resolve a problem requiring manual flight.

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Old 5th Apr 2019, 17:00
  #3339 (permalink)  
 
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The inference that manual trim was not available may not be correct, in fact the report refers to "manual electric trim" meaning the control column trim switches, this is in fact the "main electric trim", as distinct from manual trim. It is possible that the FO misunderstood the Captain's request for manual trim and attempted to trim by using the control column trim switches which not surprisingly did not work due to the operation of the cut out.

I think it is possible that the FO may have tried to use the control column switches at the Captain's request rather than winding the trim wheel due to the stress of the moment, even though he had only just selected the cut out. The FO's statement at 05:41:54 that "it is not working" would appear to me that the control column trim switch was not working, whereas if the manual wheel was jammed I'm sure he would have said something along the lines of "I can't move it" or "it is jammed".

I base this on my experience on the NG, where I have heard pilots and instructors both in simulator training and normal operations referring to trimming "manually" meaning manual operation of the electric trim switches, I've never seen anyone actually manually rotating the manual trim wheel in the aircraft during flight.
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Old 5th Apr 2019, 17:09
  #3340 (permalink)  
 
Join Date: Nov 2010
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Age: 51
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Originally Posted by fizz57 View Post
Disagree. May address the issues that caused the latest accident, but contradicts the entire concept of the 737's instrumentation system, and will invalidate the safety calculations on which certification is based, as well as possibly opening the doors to other failure modes.

The 737 instrumentation is a dual-redundant system, comprising two completely separate systems such that in the event of a single failure one completely operational system is still available. With the aid of appropriate disagreement monitors, standby instruments and checklists, pilots are trained to detect and diagnose such failures and take appropriate action.

This system was state-of-the-art at the time the 737 was launched and is still in use in smaller, non-FBW airliners. It is totally adequate for its stated task, that is to provide information to a well-trained human crew. It should never have been allowed to provide inputs to a system that will automatically drive flight control surfaces.
Respectfully, I don't agree with you. The concept of the 737 has been changed dramatically from the original 93' span/94' length, 110K Lbs to the current 117' span/118' length, 195K Lbs. Adding STS, LAM, and now MCAS also contradicts the original B737 instrumentation system. The B737 overhead panel should have been thrown out when the designed the NG, and definitely with the MAX (FYI, DC9 and B717 are the same type rating). Having a switch to deselect a faulty indicator does not open the door to other failure modes. Not having an AOA disagree light as standard is just bad/cheap design (and Boeing agrees, all their MAXes will be retrofitted, and I believe all their more recent designs use 3 AOAs). Not informing crews about MCAS was the wrong thing to do, and not having a checklist for it letting crews re-trim the aircraft to neutral before using the cut-out for MCAS failure (as opposed to regular runaway trim) IMHO was a big mistake, just like certifying MCAS working on one AOA at a time was a big mistake.
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