Final answer:
Upon reaching Alpha Floor, the FMA annunciates the engagement of the TOGA LK mode, indicating that the aircraft's auto-thrust system has automatically provided maximum thrust to maintain a safe flying speed and prevent stalling.
Step-by-step explanation:
When you reach Alpha Floor on an aircraft, the Flight Mode Annunciator (FMA) activates a mode called TOGA LK, which stands for Take-Off/Go-Around Lock. This is an auto-thrust mode that is engaged to protect the aircraft from stalling. It automatically provides maximum engine thrust to ensure the aircraft maintains a safe speed above the stalling speed (Alpha Floor protection).
The purpose of the Alpha Floor protection is to prevent the aircraft from entering an aerodynamic stall, which is a critical safety feature in modern aircraft. When this protection is activated, the pilots are alerted, and the Auto-Thrust system takes command to increase the engine thrust, even if the throttles are not manually adjusted by the pilot.
In summary, the Alpha Floor condition triggers the TOGA LK mode on the FMA as part of the aircraft's safety features to keep the aircraft flying at a safe speed.