Certified Flight Instructor - Flight Instructor Airplane Practice Exam

The behavior of a magnetic compass during acceleration or deceleration is influenced by the Earth's magnetic field and the forces acting on the aircraft. In the Northern Hemisphere, the compass can exhibit certain inaccuracies based on the aircraft's speed changes.

When the aircraft is moving on an east or west heading, the magnetic compass tends to remain more accurate because it aligns well with the Earth's magnetic field lines which are more horizontal in these directions. However, when the aircraft is accelerating or decelerating, especially on north or south headings, the compass can show significant errors due to the magnetic dip phenomenon, where the compass needle may lag or lead based on the change in the aircraft's velocity.

This means that while the compass function may not be perfectly reliable during acceleration or deceleration on north or south headings, it maintains a more accurate indication when the aircraft is heading east or west, as these headings do not involve the same horizontal and vertical components of the magnetic field that cause erratic behavior in the other situations. This distinction helps pilots to rely more on their compass readings when flying on east or west headings during speed fluctuations.