Prepared for the ICAO AWOG (Status: February 8, 1999)

by Dr.-Ing G. Greving, NAVCOM Consult, Marbach, Germany

The increasing air traffic and the lack of space for new buildings on most of the modern international airports are serious threats for ILS-operation. Because of this, more and larger buildings are established on the airport and relatively close to the runways. This is especially threatening for the increasing demand for ILS CATIII operation where the specification for the DDM-guidance parameter is most stringent at the runway for the rollout guidance of aircraft.

ICAO Annex 10 is proposing in the Attachment C that for every major construction activity on the airport, a theoretical analysis and a numerical simulation should be performed. This is to decide in advance whether the intended building is acceptable for the assigned operational category and thus be able to sustain the current performance or protect a future need.

The total ILS consists of a number of system components, namely, the hardware ground equipment (transmitters, antennas, monitors), the airborne equipment (antennas, receivers, signal processing), and last not least, the associated environment, where the wave propagation and the multipath generation takes place which eventually determine the signal in space. The safeguarding of the ILS is achieved by protection zones on the airport, i.e. the critical and sensitive areas, and by the less obvious building restriction areas, which are much larger than the protection zones covering areas outside the critical and sensitive areas and extend often outside the airport. However, the experienced ILS-engineer knows that extremely large buildings and certain assemblies of taxiing aircraft will threaten the ILS-specs even for the most advanced systems. This threat has to be minimized to the extent possible for safety purposes. One means to aid this protection is the application of advanced numerical methods together with the necessary expertise.