What type of error occurs in a magnetic compass when an aircraft accelerates while on an easterly or westerly heading?

When an aircraft accelerates while on an easterly or westerly heading, it experiences an acceleration error in the magnetic compass. This type of error occurs due to the effects of the Earth's magnetic field on the compass when the aircraft is in motion. Specifically, during acceleration on easterly or westerly headings, the compass tends to show a heading that is higher than the true heading.

This is because of the inclination of the magnetic field lines and the resultant lag in the compass card's response due to the inertia of the liquid inside the compass. Since the compass is a magnetic device that relies on the alignment with magnetic north, when the accelerative forces act, the compass can indicate a heading that does not reflect its true direction momentarily.

Understanding acceleration error is crucial for pilots, as it emphasizes the need for additional cross-checking against other navigation instruments, especially during turns, climbs, or descents, where aircraft acceleration can occur. Knowing when and how these errors manifest helps in maintaining safer flight operations.