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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-