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Session 12: Legacy Navaids

Critical and Sensitive Areas of ILS and its 3rd Height 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.

The concept and definition of critical and sensitive areas (CASA) have been implemented to protect ILS-operation from impermanent objects on airports. The technical background is to safeguard the radiated ILS-signal for the landing aircraft to be within the ICAO specifications defined in ICAO Annex 10. Qualitative definitions and some numerical examples for the CASA are given in Att. C of Annex 10. The CASA are treated as areas on the ground in 2D without any extension in the 3rd height dimension. Typically the CASA are defined in the area of the radiating ILS-antennas and extending around the RWY depending on the operational category. The differences between critical and sensitive areas are almost semantic; some states do not use 2 different areas.
It is the basis of the CASA and well known that the ILS guidance signal can be distorted by another aircraft starting from the same RWY in a mixed mode or autoland scenario. The authors have reported and discussed a case on the IFIS 2010 which almost has led to a fatal very serious accident. Recently, some states are examining past incidents as potential CASA events. Recently occurring further scenarios include:
• closely-spaced parallel RWYs typically in a distance between 200m and 300m where one RWY is used for landing and the other is used for starting
• parallel RWYs in a larger distance 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 stronger and stronger due to the horizontal polarization for the starting A/C while the field for the landing A/C becomes weaker and weaker. Another further scenario/case has been evaluated where the approaching/landing aircraft is still high in the air, but where the ILS-signal for the landing A/C has been distorted by a starting A/C and the landing A/C did not successfully capture the ILS-LOC and deviated from the extended centerline in a critical way.
For these scenarios, modelling and systematic numerical double dynamic 3D-simulation results using state-of-the-art methodology, will be presented and the physical background will be explained.
The implications will be outlined, and proposals will be recommended. These mainly comprise information, awareness, and training for the pilots and controllers and also for the instrument procedures design task.
The examples will be reported and discussed strictly anonymously.



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