4 ms·

737MAX is not nor never has been dynamically/aerodynamically unstable. Full stop. No airliner is permitted to be unstable by FAA regulations. At no point in

737MAX is not nor never has been dynamically/aerodynamically unstable. Full stop. No airliner is permitted to be unstable by FAA regulations. At no point in the flight envelope will the aircraft pitch up into a stall without pitch-up inputs, thus it is not unstable. MCAS was used to augment flight stick characteristics, namely to simulate a linear relationship between flight-stick input force and pitch-up/AoA. This was, and always has been, about single-certification and pilot UX, not anything about the stability of the airplane. Having stick forces be somewhat lower than expected at high AoA does not make the plane unstable. The linear relationship is considered ideal, but many planes such as the 757 have a similar non-linear relationship. MCAS is not anti-stall. Granted, this has widely been mis-reported. The real issue is that the MCAS system was made dramatically more powerful, and thus dangerous, over the course of development. Without a concomitant change to the reliability of MCAS inputs (namely the AoA sensors), this resulted in disaster. https://www.seattletimes.com/business/boeing-aerospace/as-the-faa-finalizes-the-737-maxs-return-is-boeings-jet-now-safe/ https://www.seattletimes.com/business/boeing-aerospace/as-th...

acqq 6y ago
Wait, wasn't MCAS used to fix two completely different flying issues, and weren't the changes introduced in the MCAS software twice, for two different points in the flight? Wasn't at least one crash caused by MCAS activation in the phase of the flight that was not even described in most of MCAS explanations initially (which reflected the decision behind the initial introduction of MCAS, not the later modifications)? Therefore I believe the interpretation that MCAS "just augments" is too simplified from what it really was supposed to do. And the current "fixes" as they are implemented (still as to keep the "water not wet" there) could still leave plane as not behaving as it should, neither with MCAS active, nor when it is not active when it was supposed to be.
- salawat 6y ago
  MCAS was introduced to handle slackening Control surface response force at high AoA in high speed high AoA situations (Wind-up turns) and low speed high AoA situations (generally landing). That type of slackening would normally disqualify an airframe from use as a Civil Transport aircraft according to the FAA final report on the matter.
salawat 6y ago
>737MAX is not nor never has been dynamically/aerodynamically unstable. Full stop. Correct in the jargonic sense. Incorrect in the colloquial. MCAS was necessary because the MAX was not compliant with Stick force response curves in high AoA flight regimes, and would experience a reversal in the pressures required to bring the plane up to a stall. So yes, it was not aerodynamically unstable, but in the layman sense there is an instability or undesired quirk being compensated for. I know we're all pedants here, but lets be productively pedantic.

acqq 6y ago

Wait, wasn't MCAS used to fix two completely different flying issues, and weren't the changes introduced in the MCAS software twice, for two different points in the flight? Wasn't at least one crash caused by MCAS activation in the phase of the flight that was not even described in most of MCAS explanations initially (which reflected the decision behind the initial introduction of MCAS, not the later modifications)? Therefore I believe the interpretation that MCAS "just augments" is too simplified from what it really was supposed to do. And the current "fixes" as they are implemented (still as to keep the "water not wet" there) could still leave plane as not behaving as it should, neither with MCAS active, nor when it is not active when it was supposed to be.

salawat 6y ago
MCAS was introduced to handle slackening Control surface response force at high AoA in high speed high AoA situations (Wind-up turns) and low speed high AoA situations (generally landing). That type of slackening would normally disqualify an airframe from use as a Civil Transport aircraft according to the FAA final report on the matter.

salawat 6y ago

>737MAX is not nor never has been dynamically/aerodynamically unstable. Full stop. Correct in the jargonic sense. Incorrect in the colloquial. MCAS was necessary because the MAX was not compliant with Stick force response curves in high AoA flight regimes, and would experience a reversal in the pressures required to bring the plane up to a stall. So yes, it was not aerodynamically unstable, but in the layman sense there is an instability or undesired quirk being compensated for. I know we're all pedants here, but lets be productively pedantic.