Definition
An Automatic Direction Finder (ADF) indicator on which the compass card (the dial showing 0–360 degrees) can be rotated by hand using a knob, allowing the pilot to manually align the card so the aircraft's current magnetic heading sits at the top of the dial. Once aligned, the needle points to the magnetic bearing to the tuned non-directional beacon (NDB).
Plain English
An ADF instrument where you can twist the numbered dial yourself so your heading lines up at the top. Once you do that, the needle points at the actual compass direction to the radio station.
Context Anchor
Seen in instrument training when learning ADF indicators and how to interpret the needle during navigation.
Derivation
Movable-card simply means the card (the rotating dial face inside the instrument) can be moved by the pilot. This contrasts with a fixed-card ADF, where the card stays put with 0 (north) always at the top.
Why Pilots Care
Reduces headwork and interpretation errors when using ADF for navigation or holding procedures.
Intuition Check
“Movable-card” does not mean the whole ADF unit moves. It means the numbered compass card on the instrument can be rotated by the pilot.
Example Sentence 1
After turning to a heading of 090, the pilot rotated the movable-card ADF so 09 sat at the top of the dial, and the needle then pointed directly at the magnetic bearing to the NDB.
Example Sentence 2
During the ADF approach the movable-card display allowed immediate identification of the station passage when the needle swung 180 degrees.