Some random observations.
On the previous flight they disconnected the stab trim system, which stopped the MCAS inputs. So it is possible to use the trim cutout switches on this system. They then reinstated the trim system, to test it, got more MCAS trim inputs, and cut it out again. Sensible idea. But still had to operate the whole flight with the stick shaker going.
The next crew were more unsure about the problem - as if they had not been briefed. They appear to have focused on the stick shaker, by putting the flaps back down. Obviously wondering if the stick shaker was correct, and they were close to the stall. And the stick shaker did stop for a while, which may add to the confusion. “Are the stall warnings correct?”, they are wondering...
Then they get all these MCAS trim forward commands, which would be a bit of a mystery. And they reverse these MCAS inputs every time, until the end. Questions: Why not use the cuttout switches? Did this not seem like a real trim runnaway, because the trim started and stopped? And why at the end stop countering the MCAS trim inputs? Only they will know.
People here saying full forward trim can be countered with elevator? Sure about that? Even if this flight had a far-forward CofG? Only time I have experienced runnaway trim in the sim, the controls were getting uncontrollable as the cuttouts were operated - and we were nowhere near max forward. (Like this incident, we were doing 250 kt.)
So we come back to the Boeing design philosophy. Was there one? Or was the MCAS stitched together without any oversight. For instance:
Do Boeing really design things, so that a single sensor failure can lead to multiple problems? Was there really no way to have an AofA oversight system, that could detect a malfunctioning AofA indicator? Could they not have a comparitor system, that detected a sensor conflict and disabled MCAS? Single sensor input and actioning was ok, when it merely operated a stick-shaker - pilots can deal with that. But now the single malfunctioning sensor is operating the flight controls....! Did anyone think of the consequenses?
Do Boeing really design a stall-trim system that can operate to full-forward trim? Really? When do we EVER give full forward trim? Should not the system have operated until a certain (safe) forward limit was reached, and stopped there? Why allow MCAS so much authority over the controls?
Did Boeing ever try the system at 320 kts, instead of at the stall? MCAS may seem like a good idea, when approaching the stall, but just what might happen at 320 kts? Did they ever test that scenario? And this is not a case of 20/20 hindsight. This is what design testing is all about - testing out all the scenarios and all the possible (and seemingly impoossible) failure modes. Was this system rushed through, so the Max could compete with the A320..?
And why did Boeing think that a stall-trim system was a good idea at all? Traditionally, stall-pushers operate on the elevators, and for good reason. A traditional stick-pusher will push, but when it relents you are still in trim, and stick forces return to normal immediately. Conversely, a stall-trimmer will push you forwards, and then leave you way out of trim in the dive - making the recovery difficult. And remember, MCAS can trim you full forwards. Have you ever tried recovering from a stall, with the trim on the forward stop...??? Me neither...!!
So where is the Boeing QRH advice, for stall recovery with the trim fully forwards? How many pilots performed that exercise in the sim, on conversion to the Max? Answer - nil. And what would happen? Anyone tried it...? I’ll give it a go next time.
And finally, how much knowledge did the next pilot have, after the incident the previous day?? Aviation authorities have reduced preflights from 60 min to 45 min, without any thought to safety. And then the same aviation authoriites placed security in the way, so instead of the crewbus taking you to the aircraft in 3 minutes, it now takes 20 minutes. So preflight time at the aircraft can be reduced from 30 minutes to 10 minutes (plus 10 minutes starting).
So what briefing did the next pilot get? There would have been no Deferred Defect (HIL), as the problem the previous day was cleared - even though we all know that a cleared defect is not a cleared defect. Swapping a box has never cleared a technical problem. ‘Tested Found Serviceable’ has never cleared a technical problem. So the Tech Log is a book of half-truths and lies. Whatever happened to the days gone by, where such problems were left open, and marked ‘please report further’?
So a cursory glance at the tech log will show no problems. Did they take off, with no idea of the problems on the prievious flight? This is the problem with the new Politically Correct tech logs - they look wonderful and clean, but may conceal a host of problems. Intermittent defects are cleared, as if they have been rectified, but eveyone knows that the problem is still lurking. But you are not allowed to alert the next crew by having an open Deferred Defect - oh, no, that would be far too logical and safe - and would attract the attention of the greedy lawyers, who are just waiting to pounce on a single incorrect pen-stroke.....
Silver.
Edited Post Script. Regarding stalls, the QRH says, quote:
“Excessive use of pitch trim may aggravate the condition, or may result in loss of control or in high structural loads.“
So why would MCAS want to put in full forward trim, if the QRH says this can lead to a loss of control....?
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