What causes the heading indicator to drift and how should this be corrected?

The heading indicator, commonly known as the directional gyro, experiences drift primarily due to precession, which is the tendency of the gyro to change its orientation over time as a result of various forces acting on it. This drift can lead to inaccuracies in the indicated heading, making it essential for pilots to periodically check the instrument against a magnetic compass, which provides a reliable reference. By comparing the heading indicator to the magnetic compass every 15 minutes, pilots can identify any discrepancies and make necessary adjustments to maintain accurate heading information during flight.

The importance of this procedure lies in the fact that the magnetic compass is not subject to precession like the heading indicator is. Regularly checking and calibrating against the magnetic compass ensures the heading indicator remains accurate and helps the pilot effectively navigate their course.