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What causes deviation error in an airplane's magnetic compass?

Metals and electrical systems inside the aircraft.

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  1. A northerly turning error
  2. Metals and electrical systems in the aircraft ✔
  3. The gap between true and magnetic north

Why: Deviation comes from magnetic influences inside the airplane, like radios, lights, the engine, and metal parts. The gap between true and magnetic north is variation, a different error.

Huh, didn't know that: Each airplane has its own compass deviation card, made by a procedure called swinging the compass.

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References

Answer: Metals and electrical systems in the aircraft. Deviation comes from magnetic influences inside the airplane, like radios, lights, the engine, and metal parts. The gap between true and magnetic north is variation, a different error.

  1. Pilot's Handbook of Aeronautical Knowledge, Chapter 16 Navigation (FAA-H-8083-25C) www.faa.gov/sites/faa.gov/files/18_phak_ch16.pdf
    Because of magnetic influences within an aircraft, such as electrical circuits, radio, lights, tools, engine, and magnetized metal parts
    Checked 2026-10-09.

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