Private Pilot Private Practice Exam

The indications of a magnetic compass are most accurate when the aircraft is in straight-and-level unaccelerated flight. This is because in these conditions, the compass is not influenced by the forces of acceleration, deceleration, or turning, which can cause magnetic deviation and lead to erroneous readings.

When an aircraft is in a straight-and-level flight, the compass aligns itself with the Earth's magnetic field without interference from the aircraft's movements. However, during turns, the compass can show a turn error known as "compass lag" or "compass lead," resulting in inaccurate readings. Similarly, when the aircraft is accelerating or decelerating, the compass indications can also be affected by the change in motion, leading to misleading information.

For these reasons, it's crucial for pilots to rely on magnetic compass indications primarily when the aircraft is in straight-and-level unaccelerated flight to ensure navigation accuracy.