What is the major source of error in the heading indicator?

The major source of error in the heading indicator is bearing friction, which can impede the ability of the indicator to provide accurate readings. Over time, the internal mechanisms of the heading indicator, such as the gyroscope, can become affected by physical resistance or friction within the bearings. This friction can cause an increase in lag or a delay in response to actual changes in heading, resulting in inaccurate readings.

Additionally, when a pilot turns the aircraft, the heading indicator needs to smoothly reflect the change in orientation. If bearings are sticky or have excessive wear, the gyroscope may not properly align, leading to erroneous heading indications and potential navigational mistakes. In practice, pilots must be aware of this potential issue and monitor their instruments regularly, making necessary corrections or adjustments as needed.

Other factors like wind direction, temperature changes, and instrument calibration can influence the overall performance of flight instruments but they do not primarily affect the heading indicator as significantly as bearing friction does.