Definition
An automatic radio-tuning relationship in which selecting a localizer (LOC) frequency on the navigation receiver simultaneously tunes the matched glide slope (GS) frequency in the UHF band. Each ILS localizer frequency in the 108.10–111.95 MHz range is paired by design with a specific glide slope frequency in the 329.15–335.00 MHz range, so the pilot only needs to set the LOC frequency to receive both signals.
Plain English
When you tune the localizer frequency for an ILS approach, the matching glide slope frequency is selected for you automatically. You only set one number, and the receiver picks up both the side-to-side and up-and-down guidance.
Context Anchor
Seen when tuning and identifying an ILS approach, especially in discussions of how airborne ILS receivers get glide slope guidance.
Derivation
‘Pairing’ here means two things linked together by design. The localizer and glide slope transmit on different bands (VHF and UHF), so without pairing the pilot would have to tune two separate radios. The pairing is a built-in shortcut.
Why Pilots Care
It reduces cockpit workload and the chance of tuning error during an instrument approach.
Intuition Check
Do not assume GS frequency pairing means the pilot normally dials in two separate frequencies. The usual action is to tune the published ILS/localizer frequency; the glide slope frequency is paired behind the scenes.
Example Sentence 1
After tuning 110.30 for the ILS approach, the matching glide slope came alive thanks to GS frequency pairing.
Example Sentence 2
Because of GS frequency pairing, only one frequency entry is needed to receive both the localizer and glide slope signals on an ILS approach.