Components and Characteristics of the Instrument Landing System (ILS)
T-45A UJPT & E2-C2 INav-04
B. Glideslope - glideslope beam transmitter is the second half of the ILS
Fig 1: FAA Instrument
approach guidance equipment
Landing System (ILS)
Provides vertical guidance to decision height for ILS categories I,
II, and IIIA when approach is equipped
NOTE: The T-45A is Category I equipped.
Reclassifies the localizer non-precision approach to precision ILS
approach. The lowest authorized ILS minimums, with all required
ground and airborne systems components operative, are:
Category I - Decision Height (DH) 200 ft and Runway Visual
Range (RVR) 2,400 ft (with touchdown zone and centerline
lighting, RVR 1800 Category A, B, C; RVR 2000 Category D)
Category II - DH 100 ft and RVR 1,200 ft
Category IIIA - RVR 700 ft
NOTE: Special authorization and equipment are required for
Category II and IIIA.
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."
These terms are not synonymous. It is important that you 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
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."
The glideslope (highly directional, shielded antenna) signal is
radiated in the direction of the localizer front course
Located 750 to 1,250 ft down the designated ILS runway
Beam width is 55 ft (+/- 5 ft) at runway threshold crossing
Building location is normally located 250 to 600 ft from runway