# ILS Localiser Question

Jamie4590 Guest

The ILS localiser comes alive at about 28nm from the airport and what altitude and speed should I be going at this point up to the start of the glide slope?

I've found that if I'm going to fast when I start descending down the glide slope I fly over it because of the exessive speed even with GLIDE activated and have to pitch down to center the glide slope. Conversly if I slow down too early it makes the final approach and landing a long slog.

Is it standard for ILS localiser signals start at 28nm out and the GS signal at about 9nm out? If not is the only way to determine the start of it by the approach plate?

CRJCapt Chief Captain

To fly a correct ILS, you need the chart. Real world Localizer is only guaranteed out to 18 NM. Normally you should be about 3000 feet AGL and within 20 miles of the airport when intercepting the Localizer. The Glideslope interception point depends on altitude, at 3000 feet AGL it would be about 10 miles. At 1500' AGL it would be about 5 miles. Normally you want to be at a reduced speed with flaps at approx. half with gear retracted. B737- 170-180 KIAS. Lower gear and remaining flaps(30 degrees for B737) at Glideslope intercept, reduce power to computed Vref for landing. No flight spoilers below 1,000 ft. AGL and no AP below 200 ft. AGL. 🙂

Jamie4590 Guest

Cheers for that, very useful. 👍

Is being left or right of the localiser by 1 or 2 dots representing the same distance in any aircraft? I know it depends on distance from the runway because as the signal becomes stronger the closer I get the more sensitive it becomes but how can I determine how far off track from the localiser I am at strategic points along the ILS path?

Jonathan (99jolegg) Chief Captain

Each point will generally represent a couple of hundred feet on the ILS indicator. The fact that there is no measure to tell you specifically suggests that you don't really need to no on an ILS approach. All you need to know as a pilot conducting an ILS approach is that you need to bank / yaw to the left or right to become on course again. As you practice either in the sim or for your actual IR / IMC license, you'll learn how far to bank and when to roll out of the bank as to avoid overcompensation.

If you mean how far ahead you are, you can either use DME or trust the OM, MM and IM on approach to gauge your distance.

OM: 4-7nm
MM: 0.5-0.8nm
IM: Threshold

If you are using beacons make sure you have them activated on the radio panel.

CRJCapt Chief Captain

The Localizer and Glideslope courses don't get more sensitive because of signal strength but because the signal constantly grows more narrow as you near the runway. On the detailed VOR/LOC receiver in the C-172, there are five dots to the left and right of center. The Jets don't show this amount of detail and it's not needed. At 5 miles each dot is about 300 feet and at .5 miles on dot is about 100 feet. Look at pages 150-153 in the PDF file below. 🙂

Jamie4590 Guest

When the middle bar is to the extreme left or right I'll bank in that direction until the bar starts to move to center then I'll slowly turn the other way. If I time it right by the time I have reverted back to the runway heading the localiser will be centered and I'm on the correct heading. I don't like banking more than 40 degrees either side of the runway heading as this is when I end up over compensating and spend the entire approach tracking the localiser and focusing on that instead of other tasks.

The Concorde ILS localiser can be captured at 'all angles' What does this mean?

Thanks for the responses guys. A 163 page PDF file devoted to instrumentation!!! Late night for me tonight! 😉

CRJCapt Chief Captain

Normally, you want to intercept the localizer with about a 30-40 degree angle. Some AP systems have a maximum intercept angle that should not be exceeded. Once on the localizer(needle centered), you should not have to bank or turn more than 10 degrees for course correction, it's very sensitive and gets more sensitive as you get closer to the runway. If your needle goes to full deflection, you need to execute the missed approach procedure. The idea is to never allow the needle to get that far from center. You should never have to bank a aircraft, in IMC conditions, more than 30 degrees(don't know about the Concorde). 🙂

earthqu8kes First Officer

i did my year long school report on the ils system and how it works

CRJCapt Chief Captain

earthqu8kes wrote:

i did my year long school report on the ils system and how it works

Those are both good sites. I'll be gone until the 19th or 20th. I'll answer any other questions(if someone else doesn't)when I return. 🙂

Jamie4590 Guest

Have a good trip! 👍

Tartanaviation First Officer

Just about the localizer. Near the outer marker, one-dot deviation will mean that you are about 500ft off from the centerline. At and around the middle marker, one dot means that you are about 150ft off of the centerline. Each dot underneath the localizer needle represents about 0.5 degrees from course.