A22.214.171.124.4. ILS Localizer Transmitter (Non-Frangible). The ILS Localizer transmitter is
sited adjacent to the localizer antenna array. It must be located at least 76.2 meters (250-feet)
from the extended runway centerline or waiver is required.
A126.96.36.199. ILS Glide Slope Antenna (Non-Frangible). The antenna mast or monitor should be
located at a minimum distance of 121.9 meters [400 feet] from the runway centerline to the
centerline of the antenna, and should not exceed 16.7 meters [55 feet] in height above the nearest
runway centerline elevation. A mast height of over 16.7 meters [55 feet] is permitted if the
minimum distance from the runway centerline is increased by 3.1 meters [10 feet] for each 305
millimeters [1 foot] the mast exceeds 16.7 meters [55 feet]. When the mast cannot, for technical or
economic reasons, be located at a minimum distance of 121.9 meters [400 feet] from the runway
centerline, the minimum distance may be reduced to not less than 76.2 meters [250 feet] from the
centerline, provided the basic mast height of 16.7 meters [55 feet] is reduced 305 millimeters [1
foot] for each 1.7 meters [5 feet] it is moved toward the runway from the 121.9-meter [400-foot]
point. Glide slope monitor units are considered part of the parent equipment. Emergency power
generators must be as close to the facilities they support as practical.
A188.8.131.52. Marker Beacons (Non-Frangible). Marker beacons support instrument approach
procedures. They are located on the runway centerline extended as noted.
A184.108.40.206.1. Outer Marker (OM) Beacon. The OM Beacon marks the point where the aircraft
should intercept the glide slope. When the OM beacon cannot be located at this point, it is
located between this point and the landing threshold, as close to this point as possible.
A220.127.116.11.2. Middle Marker (MM) Beacon. The MM beacon is located from 609.6 meters to
1,828.8 meters [2,000 to 6,000 feet] from the instrument runway threshold. It marks the point
where the glide slope intersects the DH point of a Category (CAT) I ILS.
A18.104.22.168.3. Inner Marker (IM) Beacon. The IM Beacon is located to mark the point where
the glide slope angle intersects the DH point of a CAT II ILS. An inner marker beacon is not
used on a CAT I ILS. Marker beacons must not penetrate airspace clearance surfaces defined
in this manual.
A14.2.10. Microwave Landing System (MLS) and Mobile Microwave Landing System (MMLS)
(Non-Frangible). Criteria for siting an MLS will be added upon availability. Criteria for siting MMLS
are provided within AFI 11-230, Instrument Procedures. All installations should be sited the
maximum distance from the runway centerline allowed by operational requirements but not less than
60.96 meters (200 feet). Additionally, if the system will be required to remain in service for more than
30-days, the antenna and associated operational equipment should be removed from the trailer and
installed on a small foundation that is placed so that the surface is no higher than three-inches above
grade. The anchors used to secure the equipment should be the minimum size required to meet local
A14.2.11. Mobile Navigational Aids and Communication Facilities (Non-Frangible). These units
follow the same general siting criteria as their fixed facility counterpart; and the same deviations from
standard clearance criteria are permissible. Power generators for these facilities will be located as close
to the equipment and in as small a site configuration as possible.
A14.2.12. Mobile Air Traffic Control Towers (MATCT) (Non-Frangible). At least a 152.4 meters
[500 feet] distance must be maintained between the centerline of any runway and the near edge of the
tower. Power generators may be located in positions adjacent to the MATCT. Communication
antennas to be used with these towers, which are not mounted on the facility, require the same
separation from the runway centerline as the parent equipment, fixed or mobile.