What is the purpose of a magnetic compass deviation card?

A magnetic compass deviation card serves the important purpose of listing compass errors that are caused by the magnetic fields generated within the aircraft itself. These errors can arise from various onboard instruments and components that influence the magnetic field for navigation. Since a magnetic compass depends on Earth's magnetic field to provide heading information, any interference from these onboard sources can lead to inaccuracies in navigation.

Pilots rely on the deviation card to understand and correct for these errors, ensuring that their navigational readings are as accurate as possible. This is critical for safe navigation, particularly in situations where precise heading information is imperative.

In contrast, the other options do not relate to the function of a magnetic compass deviation card. Fuel consumption management, pre-flight inspections, and maps of air traffic control zones are important aspects of aviation operations, but they do not address the specific role of the deviation card in accurately displaying compass errors.