4 ms·

As I understand it, this effect is only noticeable at very high angles of attack, and is not present in normal flight regimes. (Which is why the MCAS system onl

by lutorm 8y ago

As I understand it, this effect is only noticeable at very high angles of attack, and is not present in normal flight regimes. (Which is why the MCAS system only activates near the stall.) Having an unrecoverable stall mode is not a desirable flight characteristic, for sure, but I don't think it's unheard of. For sure it's nothing like inherently unstable airframes as used in fighter jets.

borkt 8y ago
Im pretty sure the problem is that a sensor failure is causing it to believe it is at a higher angle of attack than it actually is, but I'm only skimming.
- lutorm 8y ago
  Yes, that's the present problem. I'm referring to the inherent instability issue that was alluded to. The stick pusher / MCAS is designed to prevent the plane from getting into a state where it's unrecoverable.
salawat 8y ago
The effect I refer to as being unheard of in previous 737 hulls is the positive pitch instability. I don't want to repost the whole comment, because I think that's frowned upon, but someone did provide a link. My rather limited understanding is that the airframe certification path Boeing used was one meant for fast-tracked recertification of minor configuration changes of the same hull. The main idea being that the manufacturer need only prove that the reconfiguration meets the same or similar flight characteristic requirements as the hull it was derived from. This lets them produce/sell a technologically refreshed product without having to pass the rigorous testing normally associated with type-certifying a new airframe. The important characteristic of this is that the onus for this certification is left to the manufacturer. I do not know if the FAA actually independently confirms the recert is justified, or just plays it via honor system. Old 737 hulls definitely didn't have this characteristic onstability, or do-or-die reliance on functioning AoA sensors, so while I agree there isn't anything wrong with incorporating instability into a design to satisfy some specifications per se, I'd still contend that the addition of that instability should disqualify an airframe from being recertified as a reconfiguration of an older one, and should require more extensive testing/training before pilot's are cut loose on it. If anyone else has more accurate understanding of type certification, I'd be thrilled to learn the specifics.

by lutorm 8y ago

borkt 8y ago

Im pretty sure the problem is that a sensor failure is causing it to believe it is at a higher angle of attack than it actually is, but I'm only skimming.

lutorm 8y ago
Yes, that's the present problem. I'm referring to the inherent instability issue that was alluded to. The stick pusher / MCAS is designed to prevent the plane from getting into a state where it's unrecoverable.

salawat 8y ago

The effect I refer to as being unheard of in previous 737 hulls is the positive pitch instability. I don't want to repost the whole comment, because I think that's frowned upon, but someone did provide a link. My rather limited understanding is that the airframe certification path Boeing used was one meant for fast-tracked recertification of minor configuration changes of the same hull. The main idea being that the manufacturer need only prove that the reconfiguration meets the same or similar flight characteristic requirements as the hull it was derived from. This lets them produce/sell a technologically refreshed product without having to pass the rigorous testing normally associated with type-certifying a new airframe. The important characteristic of this is that the onus for this certification is left to the manufacturer. I do not know if the FAA actually independently confirms the recert is justified, or just plays it via honor system. Old 737 hulls definitely didn't have this characteristic onstability, or do-or-die reliance on functioning AoA sensors, so while I agree there isn't anything wrong with incorporating instability into a design to satisfy some specifications per se, I'd still contend that the addition of that instability should disqualify an airframe from being recertified as a reconfiguration of an older one, and should require more extensive testing/training before pilot's are cut loose on it. If anyone else has more accurate understanding of type certification, I'd be thrilled to learn the specifics.