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Originally Posted by safetypee
(Post 10439750)
bsieker #3326, The important aspect is that there is no change in the pitch trim position. Yes there is. The creep in the lines is too consistent for it to be random sampling errors (which are also there and clearly visible as jitter.) Thus the indications toward the end off the flight probably identifies reactivation of the elect trim, even two pulses recorded due to selecting the two switches back to an active state; either without further pilot elect trim input by choice, or due to a certification inhibit (? discussed elsewhere), or with manual elect trim, it was not strong enough to overpowered the tail forces (from the crew’s perception the latter situations were of an elect trim fail) The mention of failure of both electric and manual trim was much earlier, during the time where we assume that the cutout switches were in the cutout position. That to me is the most scary part that even for these moderate control column loads that can be held for several minutes, manual trim would not work at all. I had always assumed that in all but extreme out-of-trim situations, mechanical trim would be available. Bernd |
Originally Posted by TTail
(Post 10439778)
So the gear was raised at 1000'AGL? No doubt this crew was overwhelmed by the lights and shakers coming on....
So something was retracted, but it wasn't the flaps and probably not the gear. |
Thanks Bernd. But if, even with the wheel handle, the pilots can not turn the wheel fast enough? I understand that the elevator is the primary pitch control, but this is supposing the aircraft is trimmed accordingly. If, for some reason, the stabilizer does the opposite of what the pilot wants, the elevator becomes the secondary pitch control. An unwanted dive can only be corrected by using trim (on the 737). But with no electric trim it will take some precious time too bring the aircraft back to an atitude where the elevator is the primary pitch control again. And time was exactly what those pilots didn't have...
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Originally Posted by Rob21
(Post 10439787)
Thanks Bernd. But if, even with the wheel handle, the pilots can not turn the wheel fast enough? I understand that the elevator is the primary pitch control, but this is supposing the aircraft is trimmed accordingly. If, for some reason, the stabilizer does the opposite of what the pilot wants, the elevator becomes the secondary pitch control. An unwanted dive can only be corrected by using trim (on the 737). But with no electric trim it will take some precious time too bring the aircraft back to an atitude where the elevator is the primary pitch control again. And time was exactly what those pilots didn't have...
Bernd |
MCAS seems to be a cure that is much worse than the disease. And if you are having to resort to the manual trim you are really on a wing and a Prayer. Actually the prayer works better. |
- After autopilot engagement, there were small amplitude roll oscillations accompanied by lateral acceleration, rudder oscillations and slight heading changes; these oscillations also continued after the autopilot disengaged.
Originally Posted by YRP
(Post 10439305)
So what is the significance or cause of this item in the report? Is this the result of the AoA sensor issue leading to the autopilot trying to track spurious inputs?
Or is it an unrelated problem, something else wrong? |
Having read most of the comments on this thread, my general conclusions are:
1. The crews flying JT610 and ET302 were reasonably well trained and experienced in flying B737 aircraft. Their flying skills could be characterised as representative of the "Average Pilot" within the total population of B737 type-rated pilots. 2. The MCAS system, as implemented on the B737 MAX, is extremely dangerous and should never have been certified on a passenger carrying aircraft. If it activates due to a sensor or system fault at the 'wrong' or disadvantageous moment during a flight, the aircraft can become unrecoverable. 3. Any automatic system that is permitted to control the horizontal stabiliser of a passenger aircraft should be required to have a fully redundant (triplicated) sensor/control system. To make the B737 MAX safe/certifiable, the FAA and Boeing should consider the following steps: 1. Remove the MCAS system in its entirety. 2. To comply with FAR regulations concerning stick force as the aircraft approaches a stall AoA, Boeing should: (a) consider aerodynamic changes to the airframe; (b) develop a 'stick pusher' solution. In addition to fixing the B737 MAX, Boeing should set their designers and engineers to work on building a completely new state-of-the-art replacement for the B737. |
Originally Posted by JesusonAHarley
(Post 10439756)
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? 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. |
Originally Posted by fdr
(Post 10439742)
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. 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... |
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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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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Originally Posted by Luc Lion
(Post 10439785)
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. |
Originally Posted by positiverate20
(Post 10439806)
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)?
The same when trim cutout switches were off, we don't see any change in stab position but we still see MCAS AND command |
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
(Post 10439260)
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. 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... |
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. |
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..... |
Originally Posted by silverstrata
(Post 10439877)
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 |
Originally Posted by Luc Lion
(Post 10439775)
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. |
Why
Originally Posted by JesusonAHarley
(Post 10439756)
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? 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.... |
bisieker #3350, https://www.pprune.org/showpost.php?p=10439779&postcount=3350 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. |
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