Plain English Meaning

The magnetic compass is showing the wrong heading because electrical noise on the airframe — usually from flying through precipitation — is upsetting it.

Full Definition

False or unreliable magnetic compass indications caused by electrical disturbances acting on the compass, most commonly from precipitation static (P-static) building up on the airframe and discharging through or near the compass system. The compass card may swing, oscillate, or settle on a heading that does not reflect the aircraft's actual magnetic heading.

Context Anchor

Seen in weather and instrument flying discussions, especially when flying through precipitation or other conditions that can create on the aircraft.