Definition
The band of very high frequency (VHF) radio frequencies, from 108.1 megahertz to 111.95 megahertz, allocated for ILS localizer transmissions. Within this band, only odd-tenth decimal frequencies (for example 108.10, 108.15, 108.30, 108.35) are used for localizers, which is why specific channels rather than the full continuous range are assigned to individual ILS approaches.
Plain English
This is the range of radio frequencies that ILS localizers broadcast on. When a pilot tunes the navigation radio to one of these specific frequencies, they pick up the localizer signal that guides them down the runway centerline.
Context Anchor
Seen when studying or tuning an instrument landing system localizer frequency for an approach to a runway.
Derivation
MHz stands for megahertz, meaning millions of cycles per second. 'Mega' comes from the Greek for 'great' or 'large,' and 'hertz' is named after Heinrich Hertz, the physicist who proved radio waves exist. So 108.1 MHz means the radio wave is oscillating 108,100,000 times per second.
Why Pilots Care
Only frequencies inside this band carry usable localizer signals; tuning outside it produces no guidance.
Grounding Statement
Think of this as the radio neighborhood where localizer guidance signals are found.
Example Sentence 1
The approach chart showed a localizer frequency of 110.30 MHz, which falls within the 108.1 to 111.95 MHz band reserved for ILS localizers.
Example Sentence 2
Before starting the approach the crew confirmed the published localizer frequency fell between 108.1 and 111.95 MHz on the standby nav radio.