Glideslope - glideslope beam transmitter

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

Components and Characteristics of the Instrument Landing System (ILS)

B. Glideslope - glideslope beam transmitter

Sg 2, fr 2

Fig 1: FAA Instrument

1. Glideslope is the second half of the ILS approach guidance

Landing System (ILS)

equipment

a. Provides vertical guidance when approach is equipped

b. Reclassifies the localizer non-precision approach to precision

ILS approach

When aircraft is ILS equipped, provides option of precision

approach to a field with no PAR facility

NOTE: Glideslope is often confused with the term “Glidepath.”

Sg 2, fr 3

These terms are not synonymous. It is important that you

Glideslope/Glidepath

clearly understand the definition of these two terms.

Glideslope: “The vertical reference provided an aircraft during

approach and landing. The glideslope reference may be any of

the following: an electronic signal (ILS or MLS), visual ground

aid (such as VASI) or glideslope information provided by ATC

during a surveillance approach.”

Glidepath: “That portion of the glideslope reference signal that

intersects the localizer on an ILS approach or is provided by

ATC when established on the FAC during a PAR approach.”

d. The glideslope (highly directional shielded antenna) signal is

radiated in the direction of the localizer front course

Sg 2, fr 4-5

Glideslope Antenna

(1) Located 750 to 1,250 ft down the designated ILS runway

(2) Beam width is 55 ft (+/- 5 ft) at runway threshold crossing

height

(3) Building location is normally located 250 to 600 ft from

runway centerline

(4) Standard ILS glideslope is normally 2.5 to 3.0 degrees (may

be higher depending on local terrain)

(5) Glideslope utilizes two signal lobes projected one above the

Sg 2, fr 6-7

other. Upper lobe is modulated with 90 Hz and the lower

Glideslope Signal Lobes

lobe at 150 Hz at an equal signal strength

(6) Each lobe is approximately 0.7 degrees wide with a total

beam width of approximately 1.4 degrees wide

(7) The point of equal signal modulation sets the center of the

glideslope beam

Page 4-7

(2-02) Original