3. The system may be divided functionally into
three parts:
(a) Guidance information: localizer, glide
slope.
(b) Range information: marker beacon,
DME.
(c) Visual information: approach lights,
touchdown and centerline lights, runway lights.
4. The following means may be used to
substitute for the OM:
(a) Compass locator; or
(b) Precision Approach Radar (PAR); or
(c) Airport Surveillance Radar (ASR); or
(d) Distance Measuring Equipment (DME),
Very High Frequency Omni-directional Range
(VOR), or Nondirectional beacon fixes authorized in
the Standard Instrument Approach Procedure; or
(e) Very High Frequency Omni-directional
Radio Range (VOR); or
(f) Nondirectional beacon fixes authorized in
the Standard Instrument Approach Procedure; or
(g) A suitable RNAV system with Global
Positioning System (GPS), capable of fix identifica
tion on a Standard Instrument Approach Procedure.
5. Where a complete ILS system is installed on
each end of a runway; (i.e., the approach end of
Runway 4 and the approach end of Runway 22) the
ILS systems are not in service simultaneously.

3. The course line along the extended centerline
of a runway, in the opposite direction to the front
course is called the back course.
CAUTION-
Unless the aircraft"s ILS equipment includes reverse
sensing capability, when flying inbound on the back
course it is necessary to steer the aircraft in the direction
opposite the needle deflection when making corrections
from off-course to on-course. This "flying away from the
needle" is also required when flying outbound on the
front course of the localizer. Do not use back course
signals for approach unless a back course approach
procedure is published for that particular runway and the
approach is authorized by ATC.

4. Identification is in International Morse Code
and consists of a three-letter identifier preceded by
the letter I (  ) transmitted on the localizer
frequency.
EXAMPLE-
I-DIA

5. The localizer provides course guidance
throughout the descent path to the runway threshold
from a distance of 18 NM from the antenna between
an altitude of 1,000 feet above the highest terrain
along the course line and 4,500 feet above the
elevation of the antenna site. Proper off-course
indications are provided throughout the following
angular areas of the operational service volume:
(a) To 10 degrees either side of the course
along a radius of 18 NM from the antenna; and
(b) From 10 to 35 degrees either side of the
course along a radius of 10 NM. (See FIG 1-1-6.)
FIG 1-1-6

Limits of Localizer Coverage

b. Localizer

1. The localizer transmitter operates on one of
40 ILS channels within the frequency range of
108.10 to 111.95 MHz. Signals provide the pilot with
course guidance to the runway centerline.
RUNWAY

2. The approach course of the localizer is called
the front course and is used with other functional
parts, e.g., glide slope, marker beacons, etc. The
localizer signal is transmitted at the far end of the
runway. It is adjusted for a course width of (full scale
fly-left to a full scale fly-right) of 700 feet at the
runway threshold.

Navigation Aids

18 NM

10 NM

LOCALIZER
ANTENNA

NORMAL LIMITS OF LOCALIZER
COVERAGE: THE SAME AREA
APPLIES TO A BACK COURSE
WHEN PROVIDED.

1-1-11