ILS localisers use 108.10–111.95 MHz. See the paired glideslope range, valid channel pattern, DME band and common tuning mistakes.
In aviation and real-world flying, an instrument landing system uses 108.10–111.95 MHz for its localiser and 329.15–335.00 MHz for its glideslope. Pilots tune only the published localiser frequency; the matching glideslope channel is paired automatically. Marker beacons, where retained, transmit on 75 MHz, while associated DME uses separate UHF channels.
ILS frequency bands at a glance
An ILS uses separate radio channels for lateral and vertical guidance, with marker beacons or DME providing position or distance information where installed.
| ILS element | Frequency | Purpose |
|---|---|---|
| Localiser | 108.10–111.95 MHz | Lateral guidance towards the runway centreline |
| Glideslope or glide path | 329.15–335.00 MHz | Vertical guidance along the approach path |
| Marker beacon | 75 MHz | Passage over a fixed point on the approach |
| Associated DME | Paired channels within 962–1213 MHz | Slant-range distance where DME is provided |
The localiser is the frequency entered by the pilot. The glideslope receiver then selects the corresponding UHF channel without a separate tuning action. DME is an associated distance aid rather than one of the two directional guidance signals; our breakdown of what separates a localiser from a full ILS explains that distinction.
CAT I, CAT II and CAT III installations use the same frequency bands. Their categories describe operational capability, equipment, monitoring and permitted minima—not different radio frequencies.
What ILS frequency does the pilot tune?
The pilot tunes the localiser frequency printed for that runway and approach, normally in a NAV receiver or through the aircraft’s flight-management system.
With conventional avionics, enter the frequency in NAV1, set the published front course where the equipment requires it, and confirm the identifier. Many airliners can autotune the ILS, but the displayed frequency, course and identifier must still agree with the approach data.
A mistake we see often is treating the inbound course as another frequency. It is only the magnetic course associated with the approach. Simulator pilots can use our explanation of finding the published ILS frequency, course and identifier in chart data; real-world pilots must use approved, up-to-date operational charts and databases.
Why are only certain localiser frequencies valid?
Only 40 assigned channels within the 108.10–111.95 MHz localiser range are valid; not every frequency between those limits is an ILS channel.
The assignments use 50 kHz channel spacing in a recognisable pattern: 108.10, 108.15, 108.30, 108.35, continuing through 111.90 and 111.95. In other words, the tenths digit is odd. The nearby VHF navigation band is shared with VOR channels, so a value can fall numerically inside the broad range without being a valid localiser assignment.
Are 90 Hz and 150 Hz also ILS frequencies?
No. The 90 Hz and 150 Hz values associated with ILS are modulation tones, not carrier frequencies that a pilot tunes.
The receiver compares the depth of those two modulations to determine whether the aircraft is left or right of the localiser centreline, or above or below the glideslope. The 1020 Hz identification tone used for the station’s Morse identifier is also modulation carried by the radio signal.
Why is there no glideslope after tuning the ILS?
Receiving a localiser without a glideslope does not automatically mean the ILS frequency is wrong.
- The procedure is localiser-only: a LOC or back-course approach normally provides no usable glideslope.
- The chart and navigation data disagree: runway renumbering, old simulator data or conflicting scenery can leave the published frequency different from the one modelled.
- The aircraft is outside reliable coverage: being too close, too high or on the wrong side of the installation can prevent a valid indication.
- The avionics source is wrong: some aircraft require the display or course selector to use NAV/LOC rather than GPS guidance.
- The wrong runway-end ILS is tuned: nearby or reciprocal approaches can have different frequencies and identifiers.
Intercept the published glideslope from below rather than chasing it from above; real installations can produce false lobes above the normal path. For simulator-specific setup, our practical Microsoft Flight Simulator ILS tuning sequence covers the receiver and approach configuration.