Offset ILS

[parkfell]

What is the maximum offset allowed in the UK, and does this impact upon the maximum glidepath angle ?

:cool:

[terrain safe]

I can see that you have been inundated with replies so I thought that I would put in my 2p worth of info.

The only airfield that I know of with an offset ILS is Sumburgh, which is offset by 3 degrees, but the glidepath, one end only, is a standard 3 degrees as well. Beyond that I can't add any more I am afraid, but I am sure there are some really knowledgeable people out there who will either know a lot more or at least point you in the right direction.

[NorthSouth]

Isle of Man also has one and there was a plan to put one in at Hawarden too - don't know if that's done yet. The limit will be in ICAO Doc 8168 or some such, which I don't have to hand just at this moment.

[reynoldsno1]

The limit is 5 degrees, and doesn't affect the GP angle. IOM is offset 3.75 degrees.

Mind you, Kai Tak IGS was offset 47 degrees ISTR ....
:ooh:

[Vee One...Rotate]

Doesn't London City have a 5 or 7 degree glideslope angle? Apparently it gives the impression of a helicopter landing. Saw some cockpit footage from a 146 once - certainly looked steep!

V1R

[reynoldsno1]

London City is not offset. GP is 5.5 deg - used to be 7.5 until they lengthened the runway....

[parkfell]

Thanks for the replies.

I operate into both Isle Of Man and Sumburgh.

Flying the offset down to minima in sporty conditions with that small track adjustment at the end can sometimes prove interesting.
:cool:

[keithl]

Reynolds is Right. In case you want Chapter and Verse, I've just looked it up: Doc 8168 Vol2 Part 3 Ch23 para1.

[Mooncrest]

I think LBA used to have one of these. Prior to the completion of the runway extension in 1984, the localiser aerial for RW33 (as it was then) was sited to the left of the RW15 threshold. I suppose it would have taken too much of a battering from the 737s had it been at the end of the runway. I always wondered how the pilots were meant to interpret the information from a localiser that would appear to be way off line. I didn't know then and I don't know now :confused:

[M609]

At my beloved ( ;) ) often cold airport, the LLZ for 28 is 2 degrees off, and the GP placed 115 meters short of the THR. If you follow the ILS all the way in (and waaaay below minima) you slam into a rather boggy grass field north of the undeshoot........

But it's nothing , Mo i Rana/Rossvoll (ENRA) has a 118 degrees off LLZ/DME+MKR approach. (LLZ to circling really)

[TopBunk]

Mooncrest

The information is displayed as for a normal ILS, ie LLZ and GS deviation. Due to the offset, then the limits will be quite a bit higher, and obviously autoland is not possible!

Like with any approach, if nothing is seen at minima you go around, if you have the necessary visual elements then you disconnect the autopilot and manoeuvre the aircraft as required to make the landing.

Pretty straight forward really.

[edinv]

For the record, there used to be an ILS with an off-set LLZ at EGPH on RWY31 as it once was. Dates - 1971ish to 1776ish. Reason - during WIP building the 'new RWY'. 2nd time around 1979, when major repairs to RWY07/25 as it was known then were required.

[andyb79]

Just to jump in and hijack this a bit.

'Take me to Cuba!'

Seriously though, Why are some ILS setups offset? Is it to do with the terrain/airspace on the approach or just to do with the cost of siteing the antenna in the ideal location? Or is it some government conspiracy that i shouldnt ask about?

[M609]

Is it to do with the terrain/airspace on the approach or just to do with the cost of siteing the antenna in the ideal location?

Both, in our case.

[This is a crisis]

In the Isle of Man case its because there is not enough room to put the LLZ at the end of the runway....it is situated on the south side.

[Bear 555]

Isn't Kinloss another one? I'm sure it's the road at the '08' end which prevents a traditional site for the LLZ.

Cheers

Bear 555

[Report@Boddam]

Andyb79:

Seriously though, Why are some ILS setups offset? Is it to do with the terrain/airspace on the approach or just to do with the cost of siteing the antenna in the ideal location? Or is it some government conspiracy that i shouldnt ask about?

Answer:

Can't speak for the others but at Sumburgh its due to the fact that both ends of the runway(09-27) stick out into the sea. The full ILS on 27 and LLZ on 09 were to keep costs down.

On a nice day(!) a/c use the longer runway 15/33 which has a curved approach to 33 due to the proximity of high ground. This runway not available for fix-wing landings at night for the above reasons.

R@B

:ok: