Deviation error of the magnetic compass is caused by which of the following?

• A. Certain metals and electrical systems within the aircraft
• B. Earth's magnetic field
• C. Air density changes
• D. Wind direction

Answer: (A)

Deviation error happens because the magnetic compass is influenced by local magnetic fields created by the aircraft itself. Metals, electrical systems, and other magnets inside the airplane generate their own magnetic fields, distorting the Earth's field around the compass. This interference makes the needle point away from magnetic north by an amount that changes with heading. The Earth's magnetic field is what the compass senses overall, but the local aircraft-caused fields are what cause the deviation. Air density changes or wind direction don’t create this magnetic interference, so they don’t cause deviation.