What does controllability refer to in an aircraft?

Controllability in an aircraft specifically refers to its ability to respond to control inputs made by the pilot. This concept encompasses how effectively the pilot can maneuver the aircraft by using the flight controls, allowing for changes in pitch, roll, and yaw. Proper controllability ensures that the aircraft behaves predictably when the pilot makes adjustments, which is essential for safe flying and effective aircraft handling.

Maintaining altitude, fuel efficiency, and navigation systems, while important aspects of flight operations, do not directly pertain to the aircraft's immediate response and behavior in response to pilot commands. Therefore, controllability is fundamentally about the responsiveness and handling characteristics of the aircraft as dictated by the control inputs.