AIM
4/3/14
1−1−11
Navigation Aids
(a) 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);
(b) Special Authorization Category I.
DH 150 feet and Runway Visual Range (RVR) 1,400
feet, HUD to DH;
(c) Category II.
DH 100 feet and RVR 1,200
feet (with autoland or HUD to touchdown and noted
on authorization, RVR 1,000 feet);
(d) 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);
(e) Category IIIa.
No DH or DH below 100
feet and RVR not less than 700 feet;
(f) Category IIIb.
No DH or DH below 50
feet and RVR less than 700 feet but not less than 150
feet; and
(g) Category IIIc.
No DH and no RVR
limitation.
NOTE
−
Special authorization and equipment required for
Categories II and III.
j. Inoperative ILS Components
1. Inoperative localizer.
When the localizer
fails, an ILS approach is not authorized.
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.
k. ILS Course Distortion
1.
All pilots should be aware that disturbances to
ILS localizer and glide slope courses may occur when
surface vehicles or aircraft are operated near the
localizer or 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.
2.
ATC issues control instructions to avoid
interfering operations within ILS critical areas at
controlled airports during the hours the Airport
Traffic Control Tower (ATCT) is in operation as
follows:
(a) Weather Conditions.
Less than ceiling
800 feet and/or visibility 2 miles.
(1) Localizer Critical Area.
Except for
aircraft that land, exit a runway, depart or miss
approach, vehicles and aircraft are not authorized in
or over the critical area when an arriving aircraft is
between the ILS final approach fix and the airport.
Additionally, when the ceiling is less than 200 feet
and/or the visibility is RVR 2,000 or less, vehicle and
aircraft operations in or over the area are not
authorized when an arriving aircraft is inside the ILS
MM.
(2) Glide Slope Critical Area.
Vehicles
and aircraft are not authorized in the area when an
arriving aircraft is between the ILS final approach fix
and the airport unless the aircraft has reported the
airport in sight and is circling or side stepping to land
on a runway other than the ILS runway.
(b) Weather Conditions.
At or above ceil-
ing 800 feet and/or visibility 2 miles.
(1)
No critical area protective action is
provided under these conditions.
(2)
A flight crew, under these conditions,
should advise the tower that it will conduct an
AUTOLAND or COUPLED approach to ensure that
the ILS critical areas are protected when the aircraft
is inside the ILS MM.
EXAMPLE
−
Glide slope signal not protected.
3.
Aircraft holding below 5,000 feet between
the outer marker and the airport may cause localizer
signal variations for aircraft conducting the ILS
approach. Accordingly, such holding is not author-
ized when weather or visibility conditions are less
than ceiling 800 feet and/or visibility 2 miles.
4.
Pilots are cautioned that vehicular traffic not
subject to ATC may cause momentary deviation to
ILS course or glide slope signals. Also, critical areas
are not protected at uncontrolled airports or at airports
with an operating control tower when weather or
visibility conditions are above those requiring
protective measures. Aircraft conducting coupled or
autoland operations should be especially alert in