Definition
A maintenance procedure in which an aircraft's magnetic compass is checked and adjusted against known magnetic headings, usually on a marked compass rose on the airport surface. The aircraft is aligned to each cardinal heading in turn, and small correction screws on the compass are adjusted to minimize errors caused by the aircraft's own magnetic fields. Any remaining errors are recorded on a compass correction card mounted in the cockpit.
Plain English
Turning the aircraft to known compass directions on the ground and adjusting the compass so it reads as accurately as possible. Whatever small errors are left are written on a card the pilot can refer to in flight.
Context Anchor
Seen during aircraft maintenance, especially after a compass is installed, electrical equipment is changed, or a compass accuracy check is required.
Derivation
The term "swinging" here comes from the older nautical practice of "swinging the ship" — turning a vessel through known headings to check its compass. Aviation borrowed both the procedure and the name.
Why Pilots Care
An uncorrected compass can lead to navigation errors, especially during instrument flight or when GPS is unavailable.
Intuition Check
Do not read “swinging” as the compass needle simply moving back and forth. In this maintenance use, it means turning the aircraft to known directions so the compass can be checked and adjusted.
Example Sentence 1
After the avionics upgrade, the technician performed a compass swing on the airport's compass rose and updated the correction card.
Example Sentence 2
Before the annual inspection, the technician completed compass swinging to verify the aircraft met airworthiness standards for navigation.