What do the "GP 330.5" and "CH24X" I marked in the picture below mean? I think 330.5 is localizer independent glidepath frequency but I have no idea what CH24X means. Does anyone know the details of every letter?

The image is from AIP TURKEY AD 2 LTAF ADC chart.

enter image description here

  • $\begingroup$ Seems like they ought to be frequencies for the ILS, but different than US frequencies for navaids. $\endgroup$ Commented Aug 26, 2023 at 16:39
  • $\begingroup$ Important part is CH24X for me now. $\endgroup$
    – pilot162
    Commented Aug 26, 2023 at 16:42
  • $\begingroup$ Does your ILS receiver use channels within that range? $\endgroup$ Commented Aug 26, 2023 at 16:53
  • 2
    $\begingroup$ 24X might be a TACAN channel... those are one- to three-digit numbers plus an "X" or "Y" so it would fit, and it's believable a DME transmitter would be colocated with an ILS. $\endgroup$
    – Ralph J
    Commented Aug 26, 2023 at 17:29
  • 1
    $\begingroup$ This link would be helpful for you: aviation.stackexchange.com/questions/82204/… $\endgroup$
    – user22445
    Commented Aug 27, 2023 at 3:12

1 Answer 1


24X is the paired TACAN channel. It's paired (permanently associated) with 108.7 MHz (localizer frequency for LTAF) and 330.5 MHz (Glide Slope). See this reference. (Scroll down to see the table)

So, if I tune in the localizer frequency (108.7 MHz at LTAF) my ILS navigation equipment would automatically also tune in 330.50 MHz (the Glide Slope frequency) and, if my nav equipment also included a DME unit, I would see my distance from the DME facility, which looks like it is at the same location as the Glide Slope antenna at LTAF. If, for some reason, I did not have a separate DME unit in the aircraft, but had a separate TACAN nav unit, I could set the TACAN channel to 24X (which tunes in the DME interrogation frequency of 1048 MHz and a reply frequency of 985 MHZ) and would be able to access the DME through the TACAN unit.

There is only azimuth guidance (in addition to distance/DME info) from a TACAN unit when navigating to/from a VORTAC or TACAN station, which is not at issue in your question.

I've merged the column headings in the image below with the reference for Channel 24X.

enter image description here


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