An Instrument Landing System navigation facility in the terminal area navigation system located four to seven miles from the runways edge on the extended centerline indicating the beginning of final approach.
An LF or VHF facility installed at the site of the outer marker of an instrument landing system (ILS). abbreviation: OM Fr: radioborne extérieure
ILS marker situated on centerline of approach, about 4.5 nm (8.3 km) from runway
A marker beacon at or near the glideslope intercept altitude of an ILS approach. It is keyed to transmit two dashes per second on a 400 Hz tone, which is received aurally and visually by compatible airborne equipment. The OM is normally located four to seven miles from the runway threshold on the extended centerline of the runway.
An ILS navigation facility located four to seven miles from the runway edge on the extended centerline which indicates both aurally and visually, that the aircraft is passing over the facility and can begin its final approach.