When is it appropriate to take a reading from the magnetic compass?

Taking a reading from the magnetic compass is most accurate during level, unaccelerated flight. In this state, the aircraft is not experiencing any lateral or vertical acceleration that could interfere with the compass's operation. The magnetic compass relies on the Earth's magnetic field, and during turns, climbs, or descents, the compass can indicate erroneous readings due to the forces acting on the aircraft.

When the aircraft is level and flying straight and without acceleration, the compass aligns accurately with the magnetic field, providing the pilot with a reliable indication of the aircraft's heading. This practice ensures that navigational decisions made during flight are based on accurate compass readings, which is critical for maintaining situational awareness and adhering to course requirements.

In other scenarios, such as during cruising altitude or other flight phases, while compass readings can still be taken, they might not be as reliable as during level, unaccelerated flight. Thus, the best practice is to ensure that the aircraft is in stable, level flight to obtain the most accurate magnetic compass reading.