Compass Swing and Adjustment

What is a Compass Swing?

A compass swing is a systematic procedure used to determine and correct the deviation of an aircraft's magnetic compass. Deviation is the error caused by local magnetic fields within the aircraft, which can change due to equipment, cargo, or even the aircraft's orientation over time.

Compass Swing Procedure

• The aircraft is positioned on a compass rose or calibrated base, aligned with magnetic north, away from magnetic interference.
• The aircraft is rotated to each cardinal heading (north, east, south, west), and the compass is adjusted using compensating magnets to minimize deviation.
• After initial adjustments, the aircraft is rotated in 30° increments through a full 360° circle, and the compass deviation is measured at each heading.
• All deviations are recorded on a compass correction card, which is placed near the compass for the pilot's reference.

When is a Compass Swing Required?

A compass swing must be performed:

• After major changes to aircraft electrical or electronic systems
• Following a lightning strike
• When transferring to a location with a significant change in magnetic latitude
• After installing a new compass
• If the aircraft has been parked in one direction for an extended period
• Whenever compass readings seem unreliable or inconsistent
• As specified in the aircraft's maintenance schedule

Compass Adjustment and Calibration

Adjustment involves fine-tuning the compass using built-in compensating magnets to reduce deviation. The goal is to keep residual deviation within acceptable limits (typically ±10° for light aircraft, but often much less with proper procedure). The results are documented for operational use.

Operational Considerations

Pilots must always check the compass before flight, looking for physical damage, fluid level, and correct movement. During taxi, the compass should respond correctly to turns. If carrying magnetic cargo, extra caution is needed as it can affect compass accuracy.