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View Full Version : Official Localizer coverage [25 vs 18 nm]


zxccxz
25th Aug 2012, 19:49
Official Localizer coverage..

Which one do you use?

Jeppesen booklet says 18 nm:
http://s8.postimage.org/sn21k1dc5/jepp.gif


Icao annex 10 says 25 nm:

http://s8.postimage.org/6mlp3euo5/icao.gif

aterpster
25th Aug 2012, 21:36
Those illustrations are really meaningless. The localizer is useable for the distance set forth in any given ILS IAP. Flight inspection and facilities technicans make sure that is the case.

In some cases the localizer can be distorted sufficiently off centerline that radar vectors are mandatory.

ft
25th Aug 2012, 23:05
Normally, as per ICAO standards, localizers are commissioned to 25 nm in the course sector and 17 nm out to 35 degrees off centerline.

In the U.S., and possibly other places, frequency congestion has brought about reduced coverage localizers which are 18 nm in the course sector and 10 nm out to 35 degrees off centerline.

There are also long-range facilities in the U.S., with coverage far exceeding the normal specifications.

Cheers,
/Fred

172_driver
25th Aug 2012, 23:38
Those illustrations are really meaningless. The localizer is useable for the distance set forth in any given ILS IAP. Flight inspection and facilities technicans make sure that is the case.I have personally never seen that written in any AIP. In one I could find the range of the associated Lctr. but not the localizer. I was taught 18 nm (ICAO) and use that in my practical flying (18 nm, correct sensing, arm VOR/LOC).



I have also seen the LAX localizer for 25L/R, which extends some 45 nm to the east?

aterpster
25th Aug 2012, 23:55
172 driver:

I have personally never seen that written in any AIP. In one I could find the range of the associated Lctr. but not the localizer. I was taught 18 nm (ICAO) and use that in my practical flying (18 nm, correct sensing, arm VOR/LOC).

I have also seen the LAX localizer for 25L/R, which extends some 45 nm to the east?

More like 50 miles with the four ILSes from the east. That is called extended service volume (ESV) and requires more frequency protection and good localizer transmitters. You don't see ESV mentioned in any AIP, either.

In your practical flying if you use the localizer only where it is authorized on the approach chart, you then couldn't care less about that 18 miles.