ILS Localizer 4

28.10.2004

Submission:

I do not agree with Mr. Ivan Ferencz as to the derivation of the mentioned angle of +-7.7°. It is made from the intersection line of the so-called glide path plane assuming probably 3° nominal GP-angle and 15m TCH yielding z=0.0524x+15.00 . The formula has been slightly corrected or modified. As shortly mentioned the coverage angle radius of a Localizer is measured from the centre of the LOC-antenna. The proposed intersection line does not originate from this point. However, my main concern is related to the fact that this angle would depend on the GP-angle and on the TCH. Also, it is an intersection of an ILS-based plane (Annex 10) and an obstacle clearance based plane (Annex 14). Why ? Is there any physical and operational background for this? The OCS-definitions have basically nothing to do with the ILS-background, like type of antennas and the details of ILS-coverage. The definitions within Annex 10 for the course (+-10°) and the clearance region (+-35°) have again basically nothing to do with the hardware installations of the LOC-antennas. Today we have wide aperture dual frequency ILS LOC-antennas that have an effective course coverage of only ca. +-3° to +-4°. It is the transition angle between the hardware course and clearance radiation of the antenna. Effectively that means that the clearance subsystem of the antenna is serving coverage within the basic ILS course sector. Operationally speaking the A/C or pilot does not know from where the ILS-LOC-signal comes from (course or clearance subsystem of the LOC-antenna). The only point is that the A/C must have a valid and safe ILS-signal (proportional or fly right or left) in that region which is defined by the procedure, which includes all the remarks, and NOTAM's in the AIP and charts. There are quite a number of cases where the standard ICAO figures (+-35°, +-10°, 3°, +-8°) cannot be met. Of course you can land in the precision mode if the procedures and the navaids signals served are safely adapted to each other and if the pilot follows the procedure. So, I still be convinced that the minimum and safe required LOC-coverage can be much less than the standard +-35° : e.g. +-10° or less - it depends on the optimised design of the combination of the procedures and of the related navaids supporting the procedure. The azimuthal minimum coverage of the related ILS-glide path is proposed to be minimum +-2*LOC width. The LOC-width depends on the runway length and means DDM=150µA at 105m lateral at threshold.

Dr.-Ing. Gerhard Greving - NAVCOM Consult