Definition
The specific VHF radio frequency, between 108.10 and 111.95 MHz on odd-tenths channels, on which a runway's localizer transmits its lateral guidance signal for an ILS or LOC approach. Each instrument runway end has its own published localizer frequency that the pilot tunes into the navigation radio to receive course guidance to that runway centerline.
Plain English
The radio frequency a pilot tunes in to receive the side-to-side guidance signal that lines the aircraft up with a particular runway during an instrument approach.
Context Anchor
Seen when setting up or briefing an instrument approach, especially to parallel runways where each runway may have its own localizer frequency.
Derivation
“Localizer” comes from “localize,” meaning to determine or guide to a particular place. “Frequency” originally meant how often something happens; in radio use, it means the rate of a radio wave, which is used as a specific channel.
Why Pilots Care
Selecting the correct frequency gives the pilot reliable lateral guidance to stay aligned with the runway when visibility is low.
Intuition Check
Frequency here does not mean how often something occurs. It means the specific radio channel used to receive the localizer signal.
Example Sentence 1
Before starting the approach, the pilot tuned the localizer frequency for Runway 28L into NAV1 and identified the Morse code ident.
Example Sentence 2
The approach chart listed the localizer frequency right next to the runway information.