Originally Posted by ZeeDoktor
Only alpha floor is lost in alternate law 2.
Maybe I'm just getting confused, which wouldn't be the first time. However, my understanding is that alternate law does not maintain any of the protections in pitch, except maneuver protection. (ref. FCOM 3.04.27 P6). The normal "High angle of attack protection" is replaced by a new protection called "Low speed stability". (ref. ACA Memo P6). An aural "STALL, STALL, Stall" warning sounds at low speeds, but may also sound at high altitude where it warns that the aircraft is approaching the angle of attack for the onset of buffet. (ref. FCOM 3.04.27 P6). BEA report #2 explains that stall warning is triggered when the AoA exceeds a certain threshold that varies with Mach number. Low speed stability is described in FCOM 1.27.30 P2:
Alt 1: At low speed, a nose down demand is introduced in reference to IAS, instead of angle of attack, and alternate law changes to direct law. It is available, whatever the slats/flaps configuration, and is active from about 5 knots up to about 10 knots above the stall warning speed, depending on the aircraft's weight and slat/flaps configuration. A gentle progressive nose down signal is introduced, which tends to keep the speed from falling below these values. In addition, audio stall warning (crickets + "STALL" synthetic voice message) is activated at an appropriate margin from the stall condition. The PFD speed scale is modified to show a black/red barber pole below stall warning. Vα prot and Vα max are replaced by Vsw (stall warning speed). The α floor protection is inoperative.
Alt 2 is identical to protections in Alt 1, except that:
1. There is no bank angle protection in Alt 2 law.
2. In case of failure of 2 ADRs, there is no low speed stability.
3. In case of failure of 3 ADRs, there is no high speed stability.
My interest in collecting these quotes is just to get this complicated subject clear in my own mind. My curiosity concerns in particular the first sentence of the Low Speed Stability description: "At low speed, a nose down demand is introduced in reference to IAS, instead of angle of attack, ...". Does this apply at high altitude? What if the reference IAS is erroneous, i.e. 2 ADRs providing similar low airspeeds? Was the gear possibly down and locked before impact?