Originally Posted by
Loose rivets
Weeks ago a poster put forward a series of comments which ended with (roughly) "So MCAS is not an anti-stall device . . . but it is, sort of."
Well, that about sums up the fuzziness of the public perception. The ST article substantiated my understanding, though the arguments above are thought provoking.
3 seconds. Hmm . . . in a quiet cockpit that didn't have STS clanking around, just maybe, but not in the real world.
The terminology used in the media and this forum is frequently incorrect from a compliance perspective.
MCAS's original intent was for a part of the operating envelope where it was obvious that the issue was a longitudinal stability compliance matter. The later disclosed issue about low speed brought along the terms of anti-stall, however that is most likely the application of a incorrect term to the real issue, at least I hope so for the OEM's sake. The approach to stall requires particular longitudinal responses which the engine design would act against at increasing AOA's, so a SAS system to normalise those characteristics is reasonable even if the design was unfortunate in practice. The risks related to an unstable longitudinal stability condition would need a high reliability system with warnings, in a similar manner to say, stall warning, stick pushers etc. It is unlikely that the oversight of incorporating a SAS system without warning would have extended to the point of installing an analogue of a stick pusher system without warning of system failure. Within the rules, such systems as pushers are not specifically noted for compliance, they are mechanisms to ensure that the respective paragraph is complied with. Where that outcome has a risk that is high, then the reliability of the architecture becomes more important, as does warning of a failure of that system. The despatch relief of the MMEL would also reflect the severity of the outcome following a failure. Overlooking the fact that the design had a SAS component that doesn't appear to meet the criteria of the regs, related to static stability is one thing, a system that is introduced to meet an unstable static stability approaching or in a stall without warning or system architecture providing reliability is a completely different level of error, and one that I doubt that an OEM such as Boeing would have fallen into. THe first is bad enough, the second is unimaginable for a company that has an obligation to provide compliant products.
Expect the aircraft has a reduced static stability in parts of the envelope, but at all times it would be stable, just not compliant. If it was truly unstable at any time, then the fur would fly.