1.2.1 In the UK, ILS Critical Areas are protected at all times that an ILS is in use. Additionally, the larger ILS Sensitive Areas are protected through ATC procedures when aircraft are making an ILS approach. The size of the Sensitive Area increases as the Category (I, II or III) of operation changes in response to decreasing visibility.
1.2.2 In the United States the ILS Critical Area is not protected if the weather conditions are better than 800 ft cloud ceiling and two miles visibility, as described in the extract from the FAA Aeronautical Information
Manual (AIM) at Appendix A.
1.3 Recommendation
1.3.1 Operators should bring this information to the attention of all their crews who are likely to fly to airfields in the United States.
1.4 Additional information
1.4.1 AIC 34/1997 (Pink 141) ‘THE USE OF ILS FACILITIES IN THE UNITED KINGDOM’.
1.4.2 JAA Temporary Guidance Leaflet ‘Section Four, Operations, Part 3: Temporary Guidance Material -
Leaflet No. 23: Use Of Autoland System On ILS Category I Facilities Or Category II/III Facilities When Low Visibility Procedures (LVP) Are Not In Force.’
1.4.3 FAA Aeronautical Information Manual
http://www.faa.gov/ATpubs/AIM/index.htm