TM 1-1510-262-10
Coupling light control computer to the cross-side PFD
Selecting an alternate ATT, HDG, or NAV source on the display controller.
(10) ILS approach mode. The ILS approach mode provides for automatic intercept, capture, and tracking
of the front course localizer and glideslope signals. This allows lying a fully coupled ILS approach.
Set-up for the ILS approach mode is as follows:
(a) VHF navigation receiver control panel -- Set desired localizer frequency.
(b) V/L pushbutton selector switch (display controller) -- Depress to select LOC1 or LOC2.
(c) Course pointer (PFD) -- Set inbound course on heading dial.
(d) Heading marker (PFD) -- Set desired intercept heading for course interception.
The PFD will now display the relative position of the aircraft to the center of the localizer beam and the desired
inbound course. With the heading marker set for intercept, the heading select mode can be used to perform the
intercept. Outside the normal capture range of the localizer signal (between one and two dots on the PFD); depress-
ing the APR pushbutton switch on the light director mode selector will cause the PFD to annunciate LOC in white
and HDG in green. The aircraft will now be lying the desired heading intercept and the system will be armed for
automatic localizer beam capture. With the aircraft approaching the selected course interception, the lateral beam
sensor (LBS) is monitoring localizer beam deviation, beam rate, and true airspeed. At the computed time, the LBS
will trip and capture the localizer signal. The light control computer will drop the heading select mode and generate
the proper roll command to bank the aircraft toward the localizer beam center. When the LBS trips, the PFD will
display LOC in green. LOC will be enclosed in a white box for 5 seconds. The glideslope portion of the approach
mode is used for the automatic intercept, capture, and tracking of the glideslope beam. The beam is used to guide
the aircraft down to the runway in a linear descent. Typical glideslope beam angles vary between 2 and 3 degrees,
depending on terrain. When the glideslope mode is used as the vertical portion of the approach, it allows the pilot to
ly a fully coupled ILS approach. The mode is interlocked, so that glideslope capture is inhibited until localizer cap-
ture has occurred. As the aircraft approaches the glideslope beam, the vertical beam sensor monitors true airspeed,
vertical speed, and glideslope deviation to determine the correct capture point. At glideslope capture, the computer
drops any other vertical mode that was in use, and automatically generates a pitch command to smoothly track the
glideslope beam. Gain programming is performed on the glideslope signal to compensate for the aircraft closing on
the glideslope transmitter and beam convergence caused by the directional properties of the glideslope antenna.
Glideslope programming is normally accomplished as a function of radio altitude and vertical speed. If the radio al-
timeter is not valid, glideslope gain programming is accomplished as a function of preset height- above-the-runway
estimates and run-down as a function of true airspeed.
Cancel the ILS approach mode by:
Depressing NAV or APR pushbutton button-indicator on the light director mode selector.
Selecting a VOR frequency on the selected VHF navigation receiver control panel.
Selecting go-around mode.
Selecting standby mode.
Selecting back course mode.
Coupling light control computer to the cross-side FMS.
Selecting an alternate ATT, HDG, or NAV source on the display controller.
When the aircraft satisies the localizer track conditions, the course error signal is removed from the lateral steering
command. This leaves radio deviation, roll attitude, and lateral acceleration to track the localizer signal, and to
compensate for localizer beam standoff in the presence of a crosswind. The system will automatically compensate
for a crosswind of up to 45 degrees course error.
(11) Pitch attitude hold mode. The pitch attitude hold mode is the basic vertical light director mode. It is
activated when a light director lateral (roll) mode is selected without an accompanying vertical (pitch) mode. There
is no annunciation for pitch hold mode although the basic AP ENG annunciation is available. The pitch command
on the PFD provides the pilot with a pitch reference corresponding to the pitch attitude existing at the moment
the lateral mode was selected. This pitch reference can be changed with the touch control steering (TCS) switch
located on the control wheels. The reference pitch attitude can also be changed as a function of the pitch wheel on
the autopilot controller when the autopilot is engaged. Pitch attitude hold mode may be cancelled by selecting any
vertical mode or the automatic capture of a vertical mode.
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