Quotes from Owain Glyndwr:
"Hang on a minute! Suppose it is an A320 at say 60 tonnes - holding at 200 kts? That will be about 5.5 deg AoA with stall at 12 deg."
Yes, Owain, that's very much the speed I would expect for holding an A320 (clean) at 60T - "Green Dot" speed would be 205, which is well above VLS, and the FMGC sometimes suggests a slightly lower figure than Green Dot for holding. A level-flight pitch of about +5 or so is typical, suggesting an AoA of that value. You quote an AoA of "stall at 12 deg". Bearing in mind that AoA Protection Law is based on alpha-prot, is that figure alpha-prot, or alpha-max? (I presume the former.)
"The alphaprotect logic is a combination of alpha and rate of change of alpha, but take just alpha for the moment. You are going to need a gust of 38 fps to get to the stall..."
Agree that a sudden up-gust of 38 fps (2280 fpm) must be extremely rare, but you admit that 38 fps doesn't take phase-advance into account.
"As for why it doesn't revert to normal law, surely it cannot, because once alphaprotect has taken charge the AOA is held at the alphaprotect value?"
...Precisely the logic I'm calling into question!
