LLZ Intercept Rules of Thumb ??

[King George V]

Does anyone have any good rules of thumb for preempting your turn to intercept the LLZ on an ILS approach.

Perhaps using a co-located NDB or VOR bearing?

All Ideas appreciated.

Thanks.

[18-Wheeler]

Yep, where the ILS has an NDB on the centreline, I always dial up the NDB and use that to get an idea when we're getting close to the localiser.
It'll give you enough warning so you can figure out when to slow down, etc, without ATC having to tell you.

[moggie]

Ideally, an NDB or VOR on the airfield will allow you to calculate your displacement from the threshold by just looking at the needle.

The ILS localiser goes alive at 2.5 degress, so as you see the needle hit about 3 deg you know you are close.

If you have a locator, then you will have to apply the 1 in 60 rule. For example, if the localiser intercept is at 12 nm, that is one fifth of 60 and so 2.5 degrees divided by 5 is 0.5 nm. If the locator is at 5nm from the airfield (i.e. 7 nm from you) then divide 60 by 7 (about 8.5). Then multiply the 0.5 nm required displacement by 8.5 to get the NDB bearing that equates to the localiser alive (0.5 x 8.5 = 4.25 degrees).

However, you could also say "the locator is about halfway out so I'll double the bearing to 5 degrees" and you would not be too far out. This can also be used to work out when to turn onto the non-precision F.A.T.

My experiece says that as long as you go rate one turn as soon as the ILS localiser goes alive, then you will be pretty close. And if self positioning, put yourself onto a 45 degree intercept for the earliest possible pick up of localiser (establish early, get settled for a smooth approach).

I am talking big aeroplane techniques by the way - a delayed turn may suit for small craft.

[john_tullamarine]

The ILS ought to be viewed with a touch of jaundiced eye. There are a number of problems which can arise, especially with the ground equipment, which can suckerbait the pilot into an awkward situation.

It is not very long ago that a well regarded airline went close to putting a wide body twinjet into the water following an erroneous glideslope intercept.

Out of the quite detailed investigation into this near accident came the conclusion that one ought to position with reference to independent guidance onto the ILS to avoid most of the problems. That is to say, just selecting approach might not always be a good idea.

[BEagle]

Personally I use the TLAR technique.....

[TechFly]

Someone was introducing false interception.

I recall a Notam stating the need to fly "raw data" until 18NM/9° from the LLZ, specially with ILS CATII/III.

In any case do not follow the GS if not stabilized within the final approach course.

Cheers.

Fly safe & enjoy life.

[scanscanscan]

After several incidents on the old HKK IGS involving American heavy metal in LNAV finals with map shift and then real GS capture showing parallel off localiser descents towards the little hills, all saved by the alert radar chaps our 767 procedures were changed.
From a trust the new technology, do not resist progress or else, it became overnight do not trust it at all!!
We were now instructed to always intercept the localiser in heading with loc armed and when loc captured, only then arm the approach.
FMC map shift was a problem in Africa DAR,Central India, and Manilla on our routes and it was not always possible to actually do a raw data backup check either.