I was talking to a pilot, and he said that the alpha floor had been activated, and I did not have time to ask him to explain this. So, can you clarify my doubt, please?
Alpha floor is a thrust function which provides TOGA thrust regardless of thrust lever position in Airbus. From Airbus Technical Digest FAST 20:
Alpha Floor is a low speed protection (in normal law) which is purely an autothrust mode. When activated, it provides TOGA thrust. As the aircraft decelerates into the alpha protection range, the Alpha Floor is activated, even if the autothrust is disengaged. Activation is roughly proportional to the rate of deceleration.
... at low speeds, if a rapid avoidance manoeuvre is required to avoid terrain, windshear or another aircraft, it is safe to rapidly pull the sidestick fully aft and/or bank and hold it there. The aircraft will pitch up to max Alpha, engage TOGA thrust and climb away.
Note that this protection is only available under normal law and is lost under alternate law.
When the angle of attack limit is reached, a value which is dependent on the configuration and longitudinal wind gradient, the FMGC receives the order from the FAC. This order is only taken into account by the FMGC, if:
- Landing gear shock absorbers are extended at takeoff
- and up to 100 ft at landing
If these conditions are met, the A/THR is engaged, and the Alpha floor protection is activated. The A/THR is commanded max. consequently.
The only way to cancel alpha floor is by disengaging the A/THR function.