Hello Chris Scott, Re, "Re. Alpha Floor inhibition
Do you have access to FCOM 2.22.30? Does it mention an inhibition at speed > M0.53? "
Yes, M0.53 is mentioned in relation to an A/THR Reversion Mode, (but not a change from Nz to AoA law - that is a different matter, I think): - from 2.22.30 in an FCOM:
A/THR MODE REVERSION
For detail refer to “Speed mode protection”.
Alpha floor
The ALPHA FLOOR protection is triggered when the FMGCs receive a signal elaborated by the PRIMs. This signal is sent when the aircraft angle of attack is above a predetermined threshold function of the aircraft configuration. The A/THR is automatically activated and commands TOGA thrust regardless of thrust lever positions. This protection is available from lift off to 100 feet RA in approach.
Following indications are then provided :
– A-FLOOR on the FMA and on the EWD as long as α floor conditions are met;
– TOGA LK on the FMA when the aircraft leaves the α floor conditions.
TOGA thrust is then frozen.
A FLOOR and TOGA LK are displayed in green and surrounded by an amber flashing box.
In order to cancel the ALPHA FLOOR or TOGA LK thrust, disconnect the A/THR.
Note: Alpha Floor is inhibited :
– in case of engine failure with flaps extended
– in case of engine failure with derated TO selected
– below 100 feet at landing
– above M.53
Alpha Floor protection is lost in case of A/THR failure.
I have to say that the differences between "Alpha-prot" and "Alpha-floor" have eluded me all these years, perhaps even still !
In addition to the FCOM descriptions of both, I think there is some imprecise use of terms in the FCOM, specifically the word, "protection". The word is used in both contexts to describe "prot" and "floor" and so is informal, whereas the terms alpha-prot, (or "α prot") and alpha-floor are formal terms.
I think the words, "prot" and "floor" are being understood as inter-changeable but am thinking that they are not. I think it is significant that "alpha-floor" is discussed only in ATA22 (Autoflight) but "alpha-prot" is not. Alpha-prot is only discussed in ATA27 (Flight Controls), with "alpha-floor" only being used in the context of, and with reference to, "alpha-prot".
Put differently, I think one can be in "alpha-prot", (a pitch-law mode) without being in alpha-floor, (an A/THR mode), but one cannot be in alpha-floor without first having "gone through" alpha-prot. The schematic in the graphic above even shows this.
So you can be in "alpha-prot" at any Mach number, but alpha-floor mode is restricted as described in the para. from the FCOM.
The important key to understanding this and using all this information from a pilot's pov is to remember what Chris Scott has outlined in the discussion on "disengagement of the AoA law". Both the AirProx and the A340 2011 Events were controllable either by leaving the stick alone, (but that leaves the airplane to "select" Max AoA in a phase-advanced scenario and is therefore not a good option), or to take control to gently push the stick forward to take the airplane back to Nz law (because, as has been observed previously, one is 'unloading the wing', so to speak) and deal with the airprox on the one hand, and sort out the mess the crew of the A340 - 2011 made for themselves on the other.