Range (position) Systems

T-45C TS INav-04; ADV INav-02

Components and Characteristics of the Instrument Landing System (ILS)

II. Range (position) Systems 2.9.4.6.5.4

Sg 3, fr 2

ILS Range Information

The following systems are commonly used to identify range (position)

when flying an ILS/LOC approach

Sg 3, fr 3-5

Marker beacons

ILS Position Location

Distance Measuring Equipment (DME)

Cross-Radial

Compass Locator

The position of the aircraft on ILS/LOC approaches is very important

due to the precise nature of the approach, lower minimums, and

obstacle clearances associated with them. The pilot relies on this

information to execute specific portions of the approach and for position

in relation to the glidepath

A. Marker beacons 2.9.4.6.5.3

Sg 3, fr 6-7

Fig 1: FAA Instrument

1. Low power transmitters (2 watts - 75 MHz)

Landing System (ILS)

2. Produces a signal in an elliptical pattern

a. 1,000 ft above the antenna

b. 2,400 ft in width and 4,200 ft in length

3. Elliptical pattern (fan pattern) placement is centered and

perpendicular to the FAC

4. Normally, two marker beacons are associated with an ILS

approach, Outer Marker (OM) and Middle Marker (MM). However,

Category II and III ILS approaches may also have an Inner Marker

(IM) associated with the approach

a. Outer Marker (OM)

(1) Indicates aircraft, if at appropriate altitude, will intercept the

glidepath

(2) Identified by a coded audio tone (three dashes) and

flashing blue cockpit marker light

b. Middle Marker (MM)

(1) Intersects the glidepath at approximately 200-ft AGL and

identifies the approximate missed approach point for

Category I approaches and Category “C” Navy aircraft

Page 4-9

(2-02) Original