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Session 12: Legacy Navaids

Critical and Sensitive Areas of ILS and their 3rd Dimension - Examples, Effects and Proposals
Gerhard Greving, NAVCOM Consult, Germany; L. Nelson Spohnheimer, Spohnheimer Consulting, USA
Location: Regency Ballroom
Date/Time: Friday, Apr. 20, 9:30 a.m.

Critical and sensitive areas (CASA) have been implemented to protect ILS operation from impermanent objects on airports. The purpose is to safeguard the radiated ILS signal for the landing aircraft to be within ICAO specifications defined in ICAO Annex 10 [1]. Qualitative definitions and some numerical examples for the CASA are given in Attachment C of Annex 10. Typically the CASA are defined in the area of the radiating ILS antennas and extending around the runway (RWY) depending on the operational category. The differences between critical and sensitive areas are almost semantic; some states do not use 2 different areas. The CASA are treated as areas on the ground in 2D without any extension in the 3rd height dimension.

It is well known that the ILS guidance signal can be distorted by another aircraft starting from the same RWY. The authors have reported a case in IFIS 2012 which led almost to a fatal accident. Some states are now examining past incidents as potential CASA events. Recent operational scenarios include:
* closely-spaced parallel RWYs (e.g., 200m and 300m) where one RWY is used for landing and the other is used for starting (mixed-mode operations)
* parallel RWYs and taxiways at a larger separation of >500m
where the starting A/C has taken off but is still in the strong radiation field of the ILS Localizer. In this case, the desired/undesired signal ratio is changing negatively, because the LOC field is increasing for the starting A/C while the field for the landing A/C decreases. Another example has the approaching aircraft still high in the air, but its ILS signal has been distorted by a starting A/C, and the approaching A/C did not successfully capture the ILS LOC and deviated from the extended centerline.

Modeling and systematic simulation results for these 3 scenarios for Localizers will be presented and the physical background will be explained. The implications will be outlined, and recommendations offered. These mainly comprise information, awareness, and training for the pilots and controllers and also for the instrument procedures design task.

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