Flight Procedures
Instrument Flight
ILS Approach
Glideslope and Localizer needles are displayed on the
ADI display and HUD, and localizer deviation is
displayed on the HSI when an ILS frequency is
selected on the VOR control panel and ILS is the only
selected steering. TACAN or WYPT can be selected in
conjunction with ILS steering. In this case, TACAN or
waypoint course deviation is shown on the HSI and ILS
deviation is shown on the ADI. The HUD displays both
TACAN or waypoint steering arrow and ILS needles
(Figure 41).
The ILS approach is a precision approach in which you
are provided precise glideslope, azimuth (course), and
range information. The ILS (Figure 42) is composed of
three elements; the localizer transmitter, the glideslope
transmitter, and marker beacons. As with any
approach, you should back up the ILS approach with
any other available NAVAIDs.
The localizer transmitter provides azimuth information
to the HSI display course line, ILS selected as the only
steering selection, and the azimuth deviation bar on the
ADI display and the HUD for maintaining alignment
with the approach course. The localizer signal has a
maximum range of 18 nm from the station, if you are
within 10 degrees either side of the course centerline.
The glideslope transmitter provides glideslope
information to the glideslope deviation bar on the ADI
display and HUD. Glideslope transmitters have a
normal range of approximately 10 nm, if you are on or
near the localizer course. However, at some locations
the glideslope has been certified for an extended
service volume which exceeds 10 nm.
NOTE: Glideslope is defined as the descent angle
assigned to an approach to a given runway for obstacle
clearance and/or signal reception. Glidepath is defined
as the portion of a precision approach that intercepts
the azimuth of an ILS approach or the FAC of a PAR
approach.
When overflown, the three marker beacons (outer,
middle, and inner) provide a distance (range) reference
by sounding an aural tone and illuminating one of three
marker beacon lights on the instrument panel.
Although there are a maximum of three marker
beacons, most ILS approaches do not have all three,
and some do not use them at all. If beacons are not
present, cross-radial fixes, DME or radar is required.
The outer beacon usually marks the FAF and will often
Figure 41: ILS INDICATIONS
indicate the point of glidepath intercept. The middle
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