Capturing LOC/GS
 

Was wondering,what the max distance out from touchdown is, where we can lock onto the LOC or LOC/GS, knowing they will give us the correct indications.

on the a320 (and i suppose most other types) auto loc capture has to happen at less than 25nm. g/s when it's active and you're on the loc at the right altitude



seb

In the US the service area seems to be not less than 20nm.

The rated coverage, where the ILS signal can be considered reliable, is usually 20-25 nautical miles.

The numbers I was given a long time ago were LOC 24 miles and less,
GS 9 miles and less, for safe capture. In otherwords inside 25 for LOC and 10 for GS.

Protected ranges for LOC and GS signals are published in Jepps.

A lot further than some might imagine
 

Yes, 'tis true.

It really depends on how well the particular ILS installation is engineered.
Example.

Yeras ago, it was common practise to have ATC inform the flight to intercept the R25L localizer at KLAX at 100 miles.
Did this work?

Actually, quite well indeed.

In fact, I flew into KLAX not all that long ago, and the exact same instructions were received.

So much for max 24 miles....:ugh:

I'm talking about protected distances that make it safe to 'lock on' not how far out you can receive a flyable signal. Early one morning over Costa got a "turn left, intercept the localiser 27L" useable but you certainly wouldn't lock on to it at that distance.

Keep in mind that you can enter an extended runway centerline into the FMS, meaning you could effectively intercept the "virtual" localizer 500 miles away, if you wanted to.

Well, lets see.

Intercept, capture, and fly inbound.
Oddly enough, this is precisely what was done at greater than normal distances I mentioned above.
I don't refer to manually flying inbound, using the heading select mode of the autopilot, but actually capturing and tracking the localizer at extended distances.

Older aircraft could do this just fine.

It could well be that new(er) generation aircraft are not so adaptable, and if this is the case (rather than individual airline SOP's, which sometimes are not that well thought out), one would have to ask....why not?

Good gosh, even the 'ole B707 could capture/track the localizer at extended distances, provided of course that the ground installation was up to snuff.

ILS facilities are protected according to the following ICAO standard:
Localiser:
17NM within 35° of LLZ course
25NM within 10° of LLZ course
Glidepath:
10NM within 8° of RWY centreline

Some airport may differ which should be in the AIC
SMOC

Flew an ILS into Marham from 70nm out once, in a Victor K2 ......... cos we could and it was a VMC day!

411A
 

The differnece is SAFE to lock-on and ABLE to lock on. No two aircraft, even of the the same model, will necessarily be the same outside the protected distances.

A NAVAID should not be used for primary navigation outside it's protected range. When on the LOC and GS, you are following the ILS and therefore it shhould be considered as the primary NAVAID.

Mr B. I remember doing that as well. The Marham ILS localiser was transmitted at higher power, something to do with it being used as an emergency navaid to get battle damaged aircraft safely back across the North Sea.

Well now, imagine that
.
Clearly a few of the old(er) timers know the score.

Of course, the KLAX 25L localizer is/was the same, and indeed there were STAR's predicated on its use....fly inbound from 100 NM.

What a shame that some of the younger guys/gals just have not had the exposure to the way procedures are handled elsewhere...and yes, quite safely as well.
Such a narrow view of things aviation.

However, what really is surprising is that some of the younger folks insist they are correct when in actual fact many simply have not need exposed to ....something different.

'Why, THAT positively is not allowed' I have heard some of 'em say, when in actual fact, a particular procedure has been in use for years and years, well before the young 'uns came along, and proudly proclaimed...'it just ain't so'.
Gives me a laugh every time.

and an ils signal (loc + g/s) is controlled and calibrated very regularly by an aircraft loaded with equipment. you never see those flying the ils's from 100 nm away.

and the difference between safe and able, cited above, is the same as certified and demonstrated. a good 'ole 707 was able to do a good barrel role but wasn't certified and safe to. and the young'uns have (i think) as good an idea of what's possible with an aircraft and what's safe with one (we're carrying pax remember), as the 'ole ones when they were young'uns.

seb

Doesn't mean they couldn't calibrate it that far out though does it?

Just like Boeing could have certified flap extension on the 73 above 20000 but didn't....

Personally, I can't see the problem especially if backed up with another navaid whose coverage extends out the relevant distance.

Yet again, common-sense ought to prevail else they'll throw the rule-book at you....just like the detractors on this thread!

:ok:

don't take me wrong, i guess we all do ils captures out at 30 or more miles. it works and even well. but it won't stand in front of a court if comes to that. i'd take the ils at 75 miles if i had only that to find a field. the certification procedure is based on rates of occurence of failures. out to 25 miles the failure rate is acceptable (for the government, the insurances, ...). up to 20000 ft the rate of occurence of a flight destabilisation is acceptable (for the same people).
again if flying at 22000 ft and absolutely (for what reason i don't know ...) needed to set some flaps then i wouldn't hesitate (knowing that my flight envelope is not demonstrated to the same reliability).

the original q was about a safe capture of loc & glide signals.

as certified it's safe to 25 nm.

seb

I have a question for you, airseb...

Let us, for the sake of discussion, presume you are following a standard published arrival route, and that arrival (STAR) clearly indicates that your flight was to transistion from the enroute airway, and intercept a localizer at a DME distance of 100nm.

There it is, printed right on the chart.
Offical, and all.
Keep in mind that this routing is flight checked on a regular basis, by the regulatory authority concerned

Now, the approach controller says to follow this routing.
What do you do?
Refuse the clearance?
Ask for another routing?
Divert to your alternate?

Drop back five yards and punt?

What?

SMOC, parabellum et al (who's al?!!) are all on the right lines. I was one of the engineers responsible for the ILS at Heathrow some years ago and I can tell you that the EGLL ILS was flight checked only within the promulgated range and no more.

It did amuse us when we received complaints from crews about g/s + loc deviations outside the promulgated range...and we carried on drinking our tea...

The point is well made by many posts, it's all very well to say that the ILS receivers in the aircraft can pick up the signal but it's not certified to work beyond its promulgated range. By all means use it but don't expect it to give you a faultless signal and make sure you have a back up - as one of the previous posts suggested. Like it or not, as professional aircrew, we have to follow the rules, that's the nature of the job. Boring, maybe, but that's the label on the tin.

I could pontificate about other ILSs in other countries which may be different but I'll stick to what I know and what I've actually stuck my screwdriver/oscilloscope probe into - ooh er missus!!

Does anyone KNOW whether these 'long range' ILSs are actually promulgated/flight tested to these incredible ranges? Getting the lobes and the integrity of the signal out to such a long range would depend on a whole host of factors - nature of the terrain would be a prime problem for propagation of the signal that far.....

:ok: