Could someone please explain why an ILS for a runway would require a Back Course option when the other end also has an ILS?

I thought it would only be appropriate where only one end has an ILS.

6 minutes ago, Ray Proudfoot said:

Could someone please explain why an ILS for a runway would require a Back Course option when the other end also has an ILS?

I thought it would only be appropriate where only one end has an ILS.

Perhaps a backup method if the full ILS for a particular runway end was out of service? 

8 minutes ago, JRBarrett said:

Perhaps a backup method if the full ILS for a particular runway end was out of service? 

That makes sense. Would it cause any issues if both ends were fully operational in a sim rather than real life?

From the interquack:

A runway might require a back course if an ILS is installed on both ends of the runway but points in opposite directions. This is because smaller airports used to use a localizer that transmitted a signal in both directions to provide horizontal guidance for both sides of the runway. This allowed for cost savings.  

2 hours ago, Ray Proudfoot said:

That makes sense. Would it cause any issues if both ends were fully operational in a sim rather than real life?

I’m not sure in the sim. Another possibility is that the airport at one time had only one ILS, with a published back course approach for the opposite end of the runway. Once such a non-precision approach is designed, tested and approved by whatever national airworthiness authority controls the airport, it might be kept in the  inventory of approaches for that airport, even if a full ILS is later added. In that case, the BC approach would still be available, though rarely, (if ever) used in practice.

In all the sims I have used, P3D, XP and MSFS, the usual logic for airports which have a full ILS on opposite ends of a particular runway (that share a common frequency), is that the ILS you receive in the aircraft depends on your relative position in relation to the runway. If the runway is 06/24 (for example) and you are closer to the 06 end, you will receive the 06 localizer, and if closer to the 24 end, you will receive the 24 localizer. With this arrangement, I don’t believe it is possible to simulate a back course.

It should be possible to emulate a BC if there is only one unique ILS frequency for a given runway.

In the real world, when both ends of a runway have a full ILS which share a common localizer frequency, the tower would never activate both ILS transmitters at the same time. In fact, I don’t believe it would be possible to do that even if they wanted to, because when one ILS is active, the other end is electrically locked out from being selected.

Because of the design of a typical ILS localizer antenna system (which is technically a collinear array of yagi antennas), a back course “beam” will usually exist. Using the BC for an actual approach in IFR conditions however would only be allowed if a tested and published back course approach exists.

Jim, you’re clearly very knowledgeable about the subject. Thanks very much for such a comprehensive reply.

I shall test the ILSs at FALE (Durban, RSA) later today.

I believe I’m right in saying as part of Cathay Pacific’s simulator assessment for pilot applicants they’d have you fly an ILS departure.

That is to fly up the ILS using the localiser and glideslope after takeoff.

Im not sure of the point of that, or if it was a procedure they actually did in the real aircraft for some strange reason.

Thankfully the introduction of RNAV and integrated approach navigation in recent years has removed the need for such nonsense.

3 hours ago, jon b said:

I believe I’m right in saying as part of Cathay Pacific’s simulator assessment for pilot applicants they’d have you fly an ILS departure.

That is to fly up the ILS using the localiser and glideslope after takeoff.

Im not sure of the point of that, or if it was a procedure they actually did in the real aircraft for some strange reason.

Thankfully the introduction of RNAV and integrated approach navigation in recent years has removed the need for such nonsense.

Some procedures like this still exist, mostly in the USA. They don't have you track the glide, though.

As others have stated, ILS on both ends would normally have one active. But as stated, if one system is down, have the back course approach on both sides could definitely increase the chances of getting in if the weather was sub par. Especially if it's an area where the weather and winds are always marginal, but you need to raise the capability of getting in. Now days, GPS makes the dream work lol.

Probably my mistake as I just remember being told years ago about tracking the ILS outbound as part of a simulator assess ent for Cathay, and between me and the person telling me we had presumed it included the GS portion too, which sounded horrifying!

Just dug around for my own interest and found some historic plates for the old Kia Tak airport which indeed had a departure back tracking the LOC ( but not the GS luckily)

https://www.dropbox.com/scl/fo/0yfb59jz2p9778djf8dbn/ACbLC6ky3e2H9Tq0J2DTDPo?dl=0&e=1&preview=Departure.pdf&rlkey=j5os7dkqdy3tk6rv9udd9jkfo

Is it possible that  Flying out bound on an ILS  the needle splits in reverse...  would pressing Backcourse button swap them to a normal orientation....

Aspen used to have 2 LOCalisers  on different frq to fly up the valley on an offset back course...  I think    would help with missed approaches also I would guess .... have it all set up on app...  just in case..   Come down on one and turn and track the other offset back course to get back out the valley..

 

 

 

 

Edited September 9, 20241 yr by aerostar

On the 747-400 there is a BCRS selection on the standby artificial horizon that would make the needles work conventionally, however there was no BCRS selection on the MCP so any backcourse would need to been flown using heading select. Or more conveniently in later days by performing what’s termed an overlay approach by simply flying in LNAV.

Aircraft with HSI instruments, be that electromechanical or EHSI will always show the LOC or BCRS in correct sense to the aircraft of course.

9 hours ago, Ray Proudfoot said:

I shall test the ILSs at FALE (Durban, RSA) later today.

Looking at the ILS approaches to FALE, the ILS 06 and ILS 24 are on different frequencies, and there is no published back course approach.  Not sure what testing those approaches will prove...am I missing something?

41 minutes ago, Bob Scott said:

Looking at the ILS approaches to FALE, the ILS 06 and ILS 24 are on different frequencies, and there is no published back course approach.  Not sure what testing those approaches will prove...am I missing something?

I’m no expert. I just opened the AFCAD with ADE as the ILS info was out of date and noticed the BC option was enabled. Aivlasoft EFB didn’t like the data in the FSDG Durban scenery package.

I took off on 24 this morning and did a tear-drop approach to 06. The localiser and GS indicator on the PC-12 worked perfectly. Now whether that’s the case with aircraft with the real one I wouldn’t like to say. Plenty of brains here though.

I flew there in 2011 with Emirates in an A330 from Dubai having left Manchester the previous evening. The airport had only been open a year. Happy times. 😁

I was kinda right about the needles because the crs is still set at approach course but the BC flips the needle to the reverse crs....

Edited September 9, 20241 yr by aerostar