How often must a pilot calibrate the heading indicator?

The heading indicator in an aircraft is subject to precession, which is the gradual drift of the indicated heading over time due to mechanical or magnetic factors. Therefore, pilots must periodically calibrate the heading indicator to ensure that it provides accurate information regarding the aircraft's heading.

The frequency of calibration depends on various factors such as the type of aircraft, the quality of the heading indicator, and the current flight conditions. Pilots are trained to be aware of this drift and correct the heading indicator accordingly to maintain situational awareness and navigation accuracy. Regular checks are necessary, especially before significant course changes or when flying in challenging navigational environments.

In contrast, continuously calibrating during flight is impractical and unnecessary as the heading indicator's drift occurs over time. Calibration only before takeoff does not account for adjustments needed mid-flight. Furthermore, calibrating 'whenever they feel like it' does not establish a systematic approach, making it unreliable for flight safety.