Compass Locators

Many people ask what the difference is between an Outer Marker (OM) and a Compass Locator Outer Marker (LOM).  It is actually very simple.

Outer/Middle/Inner Markers

These marker beacons transmit a very highly focused signal straight up (vertically).  These signals are only visible to an aircraft that is located directly over the beacon transmitter.

Compass Locators

A compass locator is much like an NDB (non-directional beacon) in that it sends out a signal that allows an ADF receiver to locate its position relative to the compass locator.  The signal is not pointed just up (like a simple marker beacon), but in all directions.

A compass locator also transmits a 2-character code which identifies itself. 

LOM - Locator Outer Marker

A locator outer marker is a combination of both an outer marker beacon and a Compass Locator.  It sends out a vertical signal straight up so aircraft overhead can read their location relative to the ILS/Localizer instrument approach procedures, but it also sends out an NDB like signal that allows an aircraft to navigate towards or away from it using ADF equipment.