# Thread: Two opposite Rwy with identical ILS frequency

1. ## Two opposite Rwy with identical ILS frequency

Hello,
Wonder if someone can tell me how to tune the correct ILS freq for one rwy when the opposite rwy has the same freq. example Toronto CYYZ rwy15R - ILP and rwy33L -ITO, both share the 110.95 freq.
How to tell the nav1 and nav2 that, for example, for the rwy 15R it should tune the freq and the correct code (ILP)?
Joaquim

2. Uhm, would one runway happen to be a backcourse localizer approach?

3. What you need to do is tune the frequency, and enter the course. Then you need to listen to the ILS identifier which will output in Morse Code. ILP will be
.. .-.. .--. and ITO will be .. - ---
This should repeat itself. If you hear an E ( . ) between repeats then the station has an error and may not be giving correct information.

4. Also the transmissions are usually highly directional, so you most likely will only get the signal for the end of the runway you are approaching.

5. Whoa Hold on. If I understand the OP's message, he is dealing with a localizer backcourse, there is only 1 transmitter on the ground! Guys, read up on a instrument procedures, specifically localizer backcourses...

6. Joaquim mentions nothing about back course. It is quite common that two ends of a runway use the same frequency. Eg Birmingham EGBB has one main runway 15/33. It has the same frequency for the ILS at both ends of the runway and neither is a back course approach.

7. Originally Posted by tomenglish2000
Joaquim mentions nothing about back course. It is quite common that two ends of a runway use the same frequency. Eg Birmingham EGBB has one main runway 15/33. It has the same frequency for the ILS at both ends of the runway and neither is a back course approach.
You mean to say that one transmitter is shooting out an ILS both ways with a glide slope?

8. Originally Posted by WJH308
You mean to say that one transmitter is shooting out an ILS both ways with a glide slope?
No, there are two directional transmitters on the same frequency*, facing opposite directions. Being highly directional they don't interfere. The ID they transmit will be different -- if it were only one transmitter that would not be so.

[* Strictly speaking of course there are 4 transmitters -- 2 each of localiser and glideslope. Probably 6 counting DME as well. But all tuned in automatically by the one 'frequency' setting on the clever NAV radios.].

Regards

Pete

9. Originally Posted by Peter Dowson
No, there are two directional transmitters on the same frequency*, facing opposite directions. Being highly directional they don't interfere. The ID they transmit will be different -- if it were only one transmitter that would not be so.

[* Strictly speaking of course there are 4 transmitters -- 2 each of localiser and glideslope. Probably 6 counting DME as well. But all tuned in automatically by the one 'frequency' setting on the clever NAV radios.].

Regards

Pete
I am confused though, how do they get rid of the backcourse? Every ILS even if it doesn't have a published backcourse, still throws out a backcourse with a false glideslope.

10. In these dual installations with single frequency ILS', the tower controller selects which one will be operational at any one time which corresponds to the active runway ... they do not transmit simultaneously, or interference would result. Usually, they will also have an interlock system which would prevent both transmitters to be on-air at the same time.

As an FYI, backcourse approaches are getting to be somewhat rare in Canada, as GPS overlay approaches displace them from the approach inventory. GPS can give lower approach limits than a BC under most situations.

Regards,
Lee Smith

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