Definition

Locator outer marker (LOM). NDB compass locator, collocated with an outer marker (OM).

Source: US FAA Pilot’s Handbook of Aeronautical Knowledge

Description

The locator outer marker (LOM) is a NAVAID that comprises:

• a locator, which is a low/medium frequency NDB uses as an aid to final approach
• a marker, which is a low-powered transmitter that directs its signal upward in a narrow pattern

The LOM is placed along the flight path of the final approach, usually about 4 NM from the runway threshold (but, depending on local terrain and other considerations this may vary between 3.5 NM and 6 NM). Both facilities have limited coverage - the locator's is usually between 10 and 25 NM and the marker's is 600 m plus or minus 200 m (2 000 ft plus or minus 650 ft).

Markers provide aural identificaiton when overflown. All markers utilize a carrier frequency of 75 MHz and the identification is frequency modilated. The outer marker identification is 2 dashes per second continuously and the tones are at 400 Hz. The locator (NDB) is identified by two or three letters.

LOMs are represented on aeronautical charts by a combined locator/marker symol. The marker is oriented perpendicularly to the flight path.

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