Swinging the compass

Maintenance procedure that measures and corrects compass deviation error (PHAK ch.8).

Who:

• Only an AME may perform it (PHAK ch.8 says AMT): adjust compensating magnets or complete compass correction card.
• Deviation comes from aircraft's own magnetism and electrics.
• Not on elementary-work list (Standard 625 Appendix A): owner or pilot cannot sign off.

Procedure (PHAK ch.8, ch.16):

1. Taxi to a compass rose.
2. Engine running, normal electrical loads on (radios etc.).
3. Align to each 30° heading in turn.
4. AME adjusts compensating magnets.
5. AME records remaining error at that heading on the compass correction (deviation) card.

Ramp compass rose (PHAK ch.8):

• Lines marked every 30°.
• Oriented to magnetic north.
• Sited where magnetic interference is minimal.

Correction card (PHAK ch.16):

• Mounted in a holder near the compass.
• Pilot interpolates mentally between headings: average of the two entries.
• Example: 180° = 0, 210° = +2, so 195° = +1.

Re-swing triggers (PHAK ch.16):

• Deviation depends on heading only, not location.
• Re-swing after landing shocks, vibration, mechanical work, new equipment (change aircraft's magnetism).

Trap: chart "compass rose" (ring of radials around a VOR) is not the ramp compass rose; only the ramp one swings a compass.

Practice