ILS-glide path TCH and RDH 3

25.10.2004

Submission:

General safety requirements and, formally, the AIP require the figure of the actual RDH. The RDH is specified by ICAO Annex 10 to be 15m and is permitted to be up to 18m. The specification in itself is does not have any negative tolerances, but only positive tolerances. Real flight check measurements of the RDH have a tolerance in the order of up to 0.5m . On the other hand one must know, that the actual DDM-tolerances are caused by stationary or variable transient objects and have effects on the DDM and subsequently on the RDH. Due to the fact that it is recommended to design the RDH for 16m or 16.5m.

I suggest to publish generally 15m in the AIP as the RDH regardless of the design of the actual measured RDH. It cannot be a safety issue because the aircraft is flying slightly higher than the limiting obstacle clearance surfaces bounded to the RDH, e.g. when flying autopilot under CATIII conditions. It is clear that the runway length is a little bit shortened.

Dr.-Ing. G. Greving

NAVCOM Consult

Germany