4 ms·

Yeah, my understanding is essentially, the changes made the Max 8 not behave aerodynamically like other 737s. This would normally mean that pilots would need to

Yeah, my understanding is essentially, the changes made the Max 8 not behave aerodynamically like other 737s. This would normally mean that pilots would need to requalify on it as a new plane type, in order to legally fly one. But that's more expensive for Boeing's customers, so to make it more attractive, they decided to "paper over" the differences in behaviour with software. Fly it like any other 737, and if it starts to stall in conditions where other 737s wouldn't, the software corrects things! Except, except, like all abstractions, this one's leaky -- and they've only shifted the difference in behaviour from "stalls at angles that would surprise a 737 pilot" to "noses-down in ways that would surprise a 737 pilot" along with "can't be muscle-overridden the way the autopilot on other 737s can be".

cmurf 8y ago
It's not the autotrim that you can't fight. The plane can be trimmed (elevator surface) in such a way that pilot yoke input (stabilizer surface) cannot fight against. That is common to all 737's, and all pilots know about it. It is not that the autotrim feature can't be fought. What's new in the MAX is the autotrim doesn't terminate when the pilot gives back pressure on the yoke if MCAS senses high angle of attack, it will do an uncommanded nose down (every I think 10s). This is to compensate for the MAX engine nacelle which provides a meaningful amount of lift to cause a pitch up moment in high angles of attack, unlike previous 737's. I wonder whether the stall behavior between 737's is slightly dissimilar or very dissimilar without MCAS, between 737NG and 737 MAX? And then quantifying that difference. I also seriously wonder if it's even slightly more likely for a pilot to induce a stall as a result of not knowing about the natural uncorrected stall behavior of the new design compared to previous designs. MCAS is not my concern, it's how the plane flies without it that I wonder about. Also, WSJ is reporting that the MCAS software update mandated by the FAA in an airworthiness directive was delayed due to the nearly five week government shutdown. I'm already imagining the tweets...

cmurf 8y ago

It's not the autotrim that you can't fight. The plane can be trimmed (elevator surface) in such a way that pilot yoke input (stabilizer surface) cannot fight against. That is common to all 737's, and all pilots know about it. It is not that the autotrim feature can't be fought. What's new in the MAX is the autotrim doesn't terminate when the pilot gives back pressure on the yoke if MCAS senses high angle of attack, it will do an uncommanded nose down (every I think 10s). This is to compensate for the MAX engine nacelle which provides a meaningful amount of lift to cause a pitch up moment in high angles of attack, unlike previous 737's. I wonder whether the stall behavior between 737's is slightly dissimilar or very dissimilar without MCAS, between 737NG and 737 MAX? And then quantifying that difference. I also seriously wonder if it's even slightly more likely for a pilot to induce a stall as a result of not knowing about the natural uncorrected stall behavior of the new design compared to previous designs. MCAS is not my concern, it's how the plane flies without it that I wonder about. Also, WSJ is reporting that the MCAS software update mandated by the FAA in an airworthiness directive was delayed due to the nearly five week government shutdown. I'm already imagining the tweets...