What is the key indicator that the altitude compensator is functioning properly?

The key indicator that the altitude compensator is functioning properly is the activation of the stick shaker. The stick shaker is a safety feature designed to alert pilots of an impending stall condition. When the altitude compensator operates effectively, it maintains proper control of the aircraft's attitude and angle of attack, thereby preventing the aircraft from entering a stall situation. The stick shaker activation serves as a warning signal, indicating that the pilot is approaching critical angles of attack where a stall could occur, thus demonstrating that the altitude compensator is actively managing the aircraft's flight parameters.

The other options, while relevant to various aspects of flight safety and aircraft performance, do not directly correlate to the proper functioning of the altitude compensator. Maintaining consistent AOA readings can be influenced by numerous factors, and while engine performance stability is crucial for overall flight safety, it is not inherently linked to the altitude compensator's role. Manual override capability refers to the pilot's ability to take control in certain circumstances but does not serve as a direct indicator of the compensator's functionality.