Shared ILS frequencies

HPNPilot1200

HPNPilot1200

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Jason
My understanding has always been that even though an ILS frequency could be shared between two runways that the antenna could only transmit for one direction (localizer) at a time. Is this correct?

Going into ACK today, we were told to expect the ILS 24 approach and ATC vectored us south/southwest of the field. When west of the field, we were receiving I-RNE (ILS 6 localizer). The GNS530 auto-identified the station as I-RNE and I confirmed by monitoring the morse code.

When we reached a few miles to the southeast of the field, the GNS530 auto-identified the station as I-ACK (ILS 24 localizer) and I confirmed this by once again monitoring the morse code which was different than what I had previously heard. The signal was fine the entire way down the approach and we broke out just above minimums.

Has anyone ever experienced this before?
 
They flipped the switch while you maneuvered for the approach; a LOC can only be active for one runway at a time.
 
HPNPilot1200 said:
My understanding has always been that even though an ILS frequency could be shared between two runways that the antenna could only transmit for one direction (localizer) at a time. Is this correct?
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Yes.

Going into ACK today, we were told to expect the ILS 24 approach and ATC vectored us south/southwest of the field. When west of the field, we were receiving I-RNE (ILS 6 localizer). The GNS530 auto-identified the station as I-RNE and I confirmed by monitoring the morse code.

When we reached a few miles to the southeast of the field, the GNS530 auto-identified the station as I-ACK (ILS 24 localizer) and I confirmed this by once again monitoring the morse code which was different than what I had previously heard. The signal was fine the entire way down the approach and we broke out just above minimums.
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Where localizers share a frequency only one of the transmitters can receive power at any time. The switch had to have been moved from the runway 6 position to the runway 24 position while you were being vectored for the approach.
 
Interesting. I asked Cape Approach when I noticed the discrepancy and they said the ILS 24 was selected and they had aircraft inbound on the approach that were receiving a valid localizer signal for 24. Very strange.
 
HPNPilot1200 said:
Interesting. I asked Cape Approach when I noticed the discrepancy and they said the ILS 24 was selected and they had aircraft inbound on the approach that were receiving a valid localizer signal for 24. Very strange.
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How does the Garmin 530 ident feature handle a backcourse?
 
wsuffa said:
How does the Garmin 530 ident feature handle a backcourse?
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It only decodes the Morse code Ident received by the receiver, it doesn't know if it is a back course or front course, the Ident is the same. So early on the ILS switch in the tower must have been set to RWY 6 and later on changed to RWY 24. The ILS has a unique code for each front course.
 
The ILS has a unique code for each front course.
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That I know.

John Collins said:
It only decodes the Morse code Ident received by the receiver, it doesn't know if it is a back course or front course, the Ident is the same. So early on the ILS switch in the tower must have been set to RWY 6 and later on changed to RWY 24.
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I have a 430 - not a 530 - and was not clear whether the 530 actually decoded the morse or drew the assumed data from the database (so you could use it to audibly identify).

You have answered the question.
 
I've had this happen when they flip the switch from one localizer to the other at KMRY. Once it got more exciting when I was a safety pilot. They were landing to the west but we wanted to fly the ILS which is to the east. They flipped it over for us. We flew an approach in actual IMC and a few hundred feet above DH the tower decided to flip the switch back to the other runway. The pilot saw the NAV flag and started the missed approach just as we popped out of the side of the fog bank. The tower apologized.
 
pdonahue said:
I've had this happen when they flip the switch from one localizer to the other at KMRY. Once it got more exciting when I was a safety pilot. They were landing to the west but we wanted to fly the ILS which is to the east. They flipped it over for us. We flew an approach in actual IMC and a few hundred feet above DH the tower decided to flip the switch back to the other runway. The pilot saw the NAV flag and started the missed approach just as we popped out of the side of the fog bank. The tower apologized.
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Sounds perfect, cept for the tower's boo-boo
 
HPNPilot1200 said:
My understanding has always been that even though an ILS frequency could be shared between two runways that the antenna could only transmit for one direction (localizer) at a time. Is this correct?

Going into ACK today, we were told to expect the ILS 24 approach and ATC vectored us south/southwest of the field. When west of the field, we were receiving I-RNE (ILS 6 localizer). The GNS530 auto-identified the station as I-RNE and I confirmed by monitoring the Morse code.

When we reached a few miles to the southeast of the field, the GNS530 auto-identified the station as I-ACK (ILS 24 localizer) and I confirmed this by once again monitoring the Morse code which was different than what I had previously heard. The signal was fine the entire way down the approach and we broke out just above minimums.

Has anyone ever experienced this before?
Click to expand...

Ahh one of my favorites. Yes, there are two separate ILS approaches there. This becomes evident with how derived alternate minimums are figured.

The G/S broadcasts a signal in both directions. This can be tested and used for LOC Back-course approaches - rare though. The LOC antenna are located at the departure end of the runway (DER). They can only send the signal in one direction and one may be active at any point in time for any one runway. When flying the approach like you described they would have flipped a switch in the tower CAB and shut off the opposite LOC (the one located on the approach end of the runway you landed on) and turned on the one on the DER.

Bob
 
Were you with the Phenom today, Jason? I saw it in TEB earlier today; I know it wasn't you flying just then, but they were departing over MERIT, I think I heard, so it could have been headed toward HYA.
 
Teller1900 said:
Were you with the Phenom today, Jason? I saw it in TEB earlier today; I know it wasn't you flying just then, but they were departing over MERIT, I think I heard, so it could have been headed toward HYA.
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Nope, in the Mooney yesterday. Now that you're all over I started listening for your call sign more closely when I'm up. :)
 
Thanks for the insight, everyone. I have a feeling when I asked Cape Approach why we were receiving I-RNE (ILS 6 localizer) he called the tower soon thereafter and had them change it to 24.
 
I'm wondering if it was IMC and they were using the ILS 24 why they even had the loc switch to the back course 6 position.
 
AdamZ said:
I'm wondering if it was IMC and they were using the ILS 24 why they even had the loc switch to the back course 6 position.
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I'm not exactly sure either. The glideslope for the ILS 6 was NOTAM'd OTS but I wouldn't imagine they were flight checking it with weather close to minimums (I didn't hear a flight check or anything unusual on the approach frequency). Plus the ILS 24 is preferred due to lower mins (1800 RVR with CL & TDZ lights).
 
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