“Why can’t I switch frequency before intercepting on an ILS/GPS approach?”

Via the ATC Manual:

10.8 The Clearance and Handover

10.8.1 This is usually the final command that will be sent to an aircraft before the Approach controller issues a frequency change to Tower/Unicom as appropriate (see 10.2 above). However there are two things the approach controller must do before handing over.

10.8.2 Firstly you must ensure that the aircraft has successfully intercepted the LOC, this is especially important with parallel operations (see below). Do not confuse aircraft being established with ‘being in the cone’, aircraft must be aligned with the centreline of the runway to be established. Remember from 10.2.3, the cone is for visual reference only!


10.8.3 Secondly, you must ensure that the aircraft closure rate is ‘acceptable’. So what is ‘acceptable’? You will have to decide but here is an example scenario: if Aircraft A is established on the ILS ahead, and you have just issued the final intercept to Aircraft B, ask yourself what is their relative speed to each other? If Aircraft A is at 160kts GS (Groundspeed), and Aircraft B is intercepting at 250kts GS with only 3nm spacing, what do you think will happen? Don’t give this problem to Tower, they do not have extensive speed commands like you, slow Aircraft B down first, then hand over. All Tower can give to that aircraft is ‘maintain slowest practical speed’, this could then have a knock-on effect if you have a line of aircraft on approach.

If you were wondering why you were either…

  1. Ignored
  2. On guarded because you switched frequencies
  3. Told to check help pages
  4. Told to stay on frequency

…after you switched from the approach frequency to tower or you asked for a frequency change, this is why. We (approach) can’t let you switch frequency before the criteria above is met. Hope you find this helpful and you learn something new!


Great manual…
I have seen it before too :)

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