Definition
A Locator Outer Marker is a low-power non-directional beacon (NDB) installed at or near the outer marker position of an instrument landing system (ILS) approach. It provides bearing information that helps pilots intercept and track the final approach course toward the runway, and traditionally marked the point where the glideslope is intercepted at the published altitude.
Plain English
A small radio beacon located along the final approach path, several miles from the runway, that helps pilots find and line up with the runway during an instrument approach.
Context Anchor
Seen on instrument approach charts and in approach discussions, especially when identifying a fix near the final approach path for an ILS approach.
Derivation
Locator' because it helps the pilot locate and join the final approach course. 'Outer Marker' because it sits at the outer of the marker beacon positions on a traditional ILS, typically four to seven miles from the runway threshold.
Why Pilots Care
Gives positive position confirmation so descent and timing can begin at the proper point without relying solely on DME or GPS.
Grounding Statement
Think of the LOM as a fixed radio checkpoint near the start of the close-in part of the approach.
Intuition Check
Do not read LOM as just another name for the outer marker signal. The LOM is the locator radio beacon associated with that outer marker position.
Example Sentence 1
Cleared direct to the LOM, the pilot tuned the ADF and turned to intercept the final approach course.
Example Sentence 2
We crossed the LOM at 1800 feet and started the final descent.