6 ms·

Read to the bottom of the answer on that page. Yes, the wind-up turn issue appears to have been the motivation for the initial introduction of MCAS, but (I hav

Read to the bottom of the answer on that page. Yes, the wind-up turn issue appears to have been the motivation for the initial introduction of MCAS, but (I have read elsewhere) the first version of MCAS did not yet have the motor torque required to override the pilot's force on the controls. But a second issue was found which occurred at low speeds — the article doesn't say what it was, but I'm fairly sure I've read somewhere that there was an actual instability — and in response to which Boeing expanded the allowable amount of stabilizer movement and removed the high-g sensor condition for MCAS to activate. While I don't claim to know the truth of the matter, I think it's premature to assert forcefully and unconditionally, as you have been doing, that there was no actual instability anywhere in the flight envelope. What I recall having read is that during climb, if the pilots took the AoA to a certain point somewhat higher than the normal range, pitch-up forces would increase to an unacceptable degree. Now, I may have misunderstood, or the source (sorry, can't find it) may have been misinformed. But unless you can find me an authoritative, independent source specifically contradicting this possibility, I am not willing to dismiss it, and I don't think you should be waving it away either.

PuffinBlue 7y ago
I've been very specific in what I was saying - and I have been clear on the definition of stability. That said I accept your comment and would happily be corrected, but everything I have seen has stated that there is no inherent instability in the design of the 737 Max. What I have seen (and is widely reported) is that low speed high AoA may have increased the possibility of stall compared to how previous gen 737's behaved, but we're again not talking about stability as I've been clear to define it. That increase in the possibility of stall appears to be the reason why MCAS became more powerful and operated at these critical phases of flight. It would obviously make no sense for Boeing to design an aircraft that was unbalanced. That would increase drag and reduce fuel efficiency. It's also understandable that the large and more powerful engines, plus their slightly further forward positioning, would create a slightly higher nose up pitch when compared to the previous 737's under certain phases of flight/flight configurations. That's not to say it made the aircraft unstable or unflyable, but it would suggest a reason why MCAS might be shoved into action there, in another attempt to recreate the same handling characteristics as the previous generations. That seems far more likely to be where the greater authority for MCAS came from (it would need greater authority under that flight configuration/phase of flight). It's also far more likely that there was a simple screw-up and MCAS was given too much authority and too little breadth of input. Every bit of evidence so far suggests a fight for compromise over retaining type certification and use of MCAS. Nothing suggests inherent instability.

PuffinBlue 7y ago

I've been very specific in what I was saying - and I have been clear on the definition of stability. That said I accept your comment and would happily be corrected, but everything I have seen has stated that there is no inherent instability in the design of the 737 Max. What I have seen (and is widely reported) is that low speed high AoA may have increased the possibility of stall compared to how previous gen 737's behaved, but we're again not talking about stability as I've been clear to define it. That increase in the possibility of stall appears to be the reason why MCAS became more powerful and operated at these critical phases of flight. It would obviously make no sense for Boeing to design an aircraft that was unbalanced. That would increase drag and reduce fuel efficiency. It's also understandable that the large and more powerful engines, plus their slightly further forward positioning, would create a slightly higher nose up pitch when compared to the previous 737's under certain phases of flight/flight configurations. That's not to say it made the aircraft unstable or unflyable, but it would suggest a reason why MCAS might be shoved into action there, in another attempt to recreate the same handling characteristics as the previous generations. That seems far more likely to be where the greater authority for MCAS came from (it would need greater authority under that flight configuration/phase of flight). It's also far more likely that there was a simple screw-up and MCAS was given too much authority and too little breadth of input. Every bit of evidence so far suggests a fight for compromise over retaining type certification and use of MCAS. Nothing suggests inherent instability.