ADF

ADF (Automatic Direction Finder) is an aircraft radio receiver that determines the bearing to a Non-Directional Beacon (NDB) or commercial AM broadcast station. The ADF needle on the cockpit instrument (RMI or fixed card) points toward the station, allowing the pilot to navigate to or from it.

ADF is one of the oldest forms of radio navigation still in use. While being phased out in many regions in favor of GPS, NDB/ADF approaches remain available at some airports worldwide, particularly in developing regions.