Extract from Airbus flight crew training manual:
High AOA protection enables the PF to pull the sidestick full aft in dangerous
situations, and thus consistently achieve the best possible aircraft lift. This action
on the sidestick is instinctive, and the high AOA protection minimizes the risk of
stalls or control loss.
High AOA protection is an aerodynamic protection:
· The PF will notice if the normal flight envelope is exceeded for any
reason, because the autopitch trim will stop, the aircraft will sink to
maintain its current AOA (aPROT, strong static stability), and a significant change in aircraft behavior will occur.
If the PF then pulls the sidestick full aft, a maximum AOA (approximately corresponding to CL Max) is commanded. In addition, the speedbrakes will
automatically retract, if extended.
In addition to this aerodynamic protection, there are two more energy features:
· If ATHR is in SPEED mode, the speed cannot drop below VLS, even if the target speed is below VLS
· If the angle-of-attack still increases and reaches ALPHA Floor threshold, the A/THR triggersTOGA thrust and engages (unless in some cases of one engine-out).
In case of an emergency situation, such as Windshear or CFIT, the PF is assisted in order to optimize aircraft performance via the:
· A/THR: Adds thrust to maintain the speed above VLS
· ALPHA FLOOR: Provides TOGA thrust
· HIGH AOA protection: Provides maximum aerodynamic lift
· Automatic speedbrake retraction: Minimizes drag.
Operational Recommendations:
When flying at amax, the PF can make gentle turns, if necessary.
The PF must not deliberately fly the aircraft in alpha protection, except for brief periods, when maximum maneuvering speed is required.
If alpha protection is inadvertently entered, the PF must exit it as quickly as
possible, by easing the sidestick forward to reduce the angle-of-attack, while
simultaneously adding power (if alpha floor has not yet been activated, or has
been cancelled). If alpha floors has been triggered, it must be cancelled with the
disconnect pushbutton (on either thrust lever), as soon as a safe speed is
Note:There is a nice graphic representation of the protections activation sequence, unfortunatelly cant figure out how to paste it to the post ; sorry
