Which heading is affected by acceleration and deceleration error?

Acceleration and deceleration errors primarily affect headings that are aligned with the East or West due to the nature of how magnetic compasses operate in relation to the Earth's magnetic field and the forces acting on the aircraft. When an aircraft accelerates while flying an East or West heading, the compass tends to show a turn toward the North; conversely, during deceleration, the compass will often indicate a turn toward the South.

This is a result of the compass taking time to settle down and accurately reflect the true heading of the aircraft, leading to a discrepancy known as "turning error." The effect is particularly pronounced at East or West headings because these are orthogonal to the magnetic north-south line and the compass needle's movement is more susceptible to the inertia created from acceleration and deceleration.

Other headings, such as North or South, do not exhibit this error to the same extent, as the magnetic compass aligns more directly with the Earth’s magnetic field along these lines. Therefore, East or West headings are the most affected by acceleration and deceleration errors, which perfectly clarifies why this answer is the most accurate choice in the context of the question.