How is magnetic deviation defined?

Magnetic deviation is defined as the angle through which a compass needle is deflected from the magnetic meridian due to local magnetic fields and influences within the aircraft, such as metal components or electrical equipment. This deviation is specific to each individual compass and can vary depending on the aircraft's position and the distribution of magnetic forces around it. Unlike magnetic variation, which is a global phenomenon relating to the difference between true north and magnetic north, deviation is more localized and influenced by the aircraft's own environment.

Understanding magnetic deviation is crucial for pilots since it affects compass accuracy. Pilots must consider this deflection when navigating to ensure the indicated heading aligns with the true heading that corresponds to their navigational charts. This awareness helps to maintain course accuracy and is vital for effective flight operations.