Definition
A low-power, low- or medium-frequency (L/MF) radio beacon installed at the site of the outer or middle marker of an instrument landing system (ILS). It transmits an identification signal that can be received by an aircraft's automatic direction finder (ADF), allowing the pilot to use it for navigation, holding, and as an aid during the ILS approach. The outer compass locator is typically usable within at least 15 nautical miles, and the middle compass locator within at least 5 nautical miles.
Plain English
A small radio beacon placed at one of the marker beacons on an ILS approach. The pilot tunes it on the ADF and uses it to find the approach course, hold, or back up the ILS.
Context Anchor
Seen on some instrument approach charts and approach procedures, especially where an approach has an outer or middle marker point.
Derivation
Called a 'locator' because its job is to help the pilot locate and join the ILS final approach course. 'Compass' refers to its use with the ADF, an instrument that points like a compass needle toward the tuned station.
Why Pilots Care
It gives pilots an initial course to intercept the localizer, reducing workload and increasing safety during low-visibility approaches.
Grounding Statement
The beacon sends out a continuous radio signal; the ADF needle points toward the beacon, showing the direction the aircraft must fly to reach it.
Intuition Check
Do not read this as a device that locates the aircraft’s compass. In this context, it is a radio beacon that helps the pilot locate the direction to a fixed point on an approach.
Example Sentence 1
The approach plate showed a compass locator at the outer marker, so the pilot tuned it on the ADF as a backup to the ILS.
Example Sentence 2
During the ILS approach in low ceilings, the compass locator provided reliable bearing guidance until the localizer came alive.