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AIM

10/12/17

1

−1−12

Navigation Aids

i. ILS Minimums

1.

The lowest authorized ILS minimums, with

all required ground and airborne systems components
operative, are:

(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 non

−precision

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.

Official weather

observation is a ceiling of less than 800 feet and/or
visibility 2 miles.

(1) Localizer Critical Area

. Except for

aircraft that land, exit a runway, depart, or execute a
missed approach, vehicles and aircraft are not
authorized in or over the critical area when an arriving
aircraft is inside the outer marker (OM) or the fix
used in lieu of the OM. Additionally, whenever the
official weather observation is a ceiling of less than
200 feet or RVR less than 2,000 feet, do not authorize
vehicles or aircraft operations in or over the area
when an arriving aircraft is inside the MM, or in the
absence of a MM, ½ mile final.

(2) Glide Slope Critical Area.

Do not

authorize vehicles or aircraft operations in or over the
area when an arriving aircraft is inside the ILS outer
marker (OM), or the fix used in lieu of the OM, unless
the arriving aircraft has reported the runway in sight
and is circling or side

−stepping to land on another

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.

EXAMPLE

Denver Tower, United 1153, Request Autoland/Coupled
Approach (runway)
ATC replies with:
United 1153, Denver Tower, Roger, Critical Areas 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 autho-