8. Compass Locator
8.1 Compass locator transmitters are often situated at the middle and outer marker sites. The transmitters have a power of less than 25 watts, a range of at least 15 miles, and operate between 190 and 535 kHz. At some locations, higher.powered radio beacons, up to 400 watts, are used as outer marker compass locators. These generally carry Transcribed Weather Broad-cast (TWEB) information.
8.2
Compass locators transmit two.letter identifica-tion groups. The outer locator transmits the first two letters of the localizer identification group, and the middle locator transmits the last two letters of the localizer identification group.
9.
ILS Frequency
9.1 The frequency pairs in TBL ENR 4.1.2 are allocated for ILS.
TBL ENR 4.1.2
Frequency Pairs Allocated for ILS
Localizer MHz Glide Slope
108.10 334.70
108.15 334.55
108.3 334.10
108.35 333.95
108.5 329.90
108.55 329.75
108.7 330.50
108.75 330.35
108.9 329.30
108.95 329.15
109.1 331.40
109.15 331.25
109.3 332.00
109.35 331.85
109.50 332.60
109.55 332.45
109.70 333.20
109.75 333.05
109.90 333.80
109.95 333.65
110.1 334.40
110.15 334.25
110.3 335.00
110.35 334.85
110.5 329.60
110.55 329.45
110.70 330.20
110.75 330.05
110.90 330.80
110.95 330.65
111.10 331.70
111.15 331.55
111.30 332.30
111.35 332.15
111.50 332.9
111.55 332.75
111.70 333.5
111.75 333.35
111.90 331.1
111.95 330.95
Federal Aviation Administration Twentieth Edition
10. ILS Minimums
10.1 The lowest authorized ILS minimums, with all required ground and airborne systems components operative, are:
10.1.1 Category I. Decision Height (DH) 200 feet and Runway Visual Range (RVR) 2,400 feet (with touchdown zone and centerline lighting, RVR 1,800 feet), or (with Autopilot or FD or HUD, RVR 1,800 feet);
10.1.2 Special Authorization Category I. DH 150 feet and Runway Visual Range (RVR) 1,400 feet, HUD to DH;
10.1.3 Category II. DH 100 feet and RVR 1,200 feet (with autoland or HUD to touchdown and noted on authorization, RVR 1,000 feet);
10.1.4 Special Authorization Category II with Reduced Lighting. DH 100 feet and RVR 1,200 feet with autoland or HUD to touchdown and noted on authorization, (touchdown zone, centerline lighting and ALSF.2 are not required);
10.1.5 Category IIIa. No DH or DH below 100 feet and RVR not less than 700 feet;
10.1.6 Category IIIb. No DH or DH below 50 feet and RVR less than 700 feet but not less than 150 feet; and
10.1.7 Category IIIc. No DH and no RVR limitation.
NOTE.
Special authorization and equipment are required for Category II and III.
11. Inoperative ILS Components
11.1 Inoperative Localizer. When the localizer fails, an ILS approach is not authorized.
11.2 Inoperative Glide Slope. When the glide slope fails, the ILS reverts to a nonprecision localizer approach.
REFERENCE.
See the Inoperative Component Table in the U.S. Government Terminal Procedures Publication (TPP) for adjustments to minimums due to inoperative airborne or ground system equipment.
12. ILS Course Distortion
12.1 All pilots should be aware that disturbance to ILS localizer/glide slope courses may occur when surface vehicles/aircraft are operated near the localizer/glide slope antennas. Most ILS installations are subject to signal interference by either surface vehicles, aircraft, or both. ILS “CRITICAL AREAS” are established near each localizer and glide slope antenna.
12.2 Air traffic control issues control instructions to avoid interfering operations within ILS critical areas at controlled airports during the hours the airport traffic control tower is in operation as follows:
12.2.1 Weather Conditions. At or above 800 feet and/or visibility 2 miles.
12.2.1.1 No critical area protection action is provided.
12.2.1.2 If an aircraft advises the TOWER that an “AUTOLAND”/“COUPLED” approach will be conducted, an advisory will be promptly issued if a vehicle/aircraft will be in or over a critical area when the arriving aircraft is inside the ILS middle marker.
EXAMPLE.
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