Definition
An aircraft radio navigation receiver that automatically determines the bearing to a selected ground-based non-directional beacon (NDB) or other low/medium-frequency radio station, displaying the relative bearing on a cockpit indicator.
Plain English
A cockpit instrument that points toward a chosen radio station on the ground, so the pilot can see which direction that station lies relative to the aircraft's nose.
Context Anchor
Seen in older radio navigation, instrument training, and procedures that use ground radio beacons.
Derivation
Direction finder describes what the equipment does -- it finds the direction to a radio source. Automatic distinguishes it from earlier manual direction finders, where the pilot had to rotate a loop antenna by hand and listen for the weakest signal to determine the bearing. The ADF performs that work continuously and on its own.
Why Pilots Care
Allows pilots to navigate to or from non-directional beacons, providing backup navigation when other systems fail.
Intuition Check
Automatic does not mean the airplane navigates or flies itself. Here, automatic means the equipment automatically shows the direction to the tuned radio station.
Example Sentence 1
With the ADF tuned to the local NDB, the needle swung to the 3 o'clock position, confirming the station was off the right wing.
Example Sentence 2
During the approach, the ADF provided reliable guidance when GPS was unavailable.