Definition
The procedure of adjusting the small compensating magnets inside a magnetic compass to cancel out, as much as possible, the magnetic deflections caused by ferrous metal parts and electrical currents in the aircraft itself. Any errors that remain after compensation are recorded on a compass correction card mounted near the instrument.
Plain English
Tuning the aircraft's compass so that the metal and electrical equipment around it pull on the needle as little as possible. Whatever small errors are left over are written on a card next to the compass so the pilot can apply them in flight.
Context Anchor
Seen during magnetic compass installation or maintenance, and when using the compass correction card in the cockpit.
Derivation
Compensation comes from the Latin compensare, 'to balance out' or 'to offset.' In compass work, the small magnets inside the instrument are adjusted to balance out the unwanted magnetic pull of the airframe.
Why Pilots Care
Accurate headings are required for navigation and instrument flight; uncorrected deviation can lead to heading errors of several degrees.
Intuition Check
Compass compensation does not mean the compass has been made perfect. It means aircraft-caused error has been reduced as much as practical, and any remaining error has been measured and recorded.
Example Sentence 1
After installing the new radios, the mechanic performed a compass compensation and updated the correction card.
Example Sentence 2
After installing new radios, the pilot scheduled compass compensation to ensure the heading indicator remained reliable.