With the APR mode armed, the pitch axis can be
in any one of the other pitch modes except go-around.
When reaching the vertical beam sensor trip point, the
system automatically switches to the glideslope mode.
APR ARM annunciators
extinguish and APR CAP annunciator illuminates on
the controller. At capture, a command is generated to
Capture can be made from above or below the beam.
The glideslope gain is programmed as a function of
radio altitude, time and airspeed. The APR CAP
annunciator on the mode selector will extinguish if the
GS receiver becomes invalid after capture.
Glideslope capture is interlocked so that the
localizer must be captured prior to glideslope capture.
If the glideslope receiver is not valid prior to capture,
the vertical beam sensor will not trip and the system
will remain in the pitch mode. After capture, if the NAV
receiver, GS receiver, compass data or vertical gyro
becomes invalid, ADI command cue will bias out of
view. If the radio altimeter is not valid, the glideslope
gain programming will be a function of GS capture,
time and airspeed.
While in the localizer approach mode, the pilot is
able to use a Flight Management System (FMS)
preprogrammed runway/outer marker waypoint for
reference, by pressing the OMEGA DIST/BGR switch,
located on the pilot's instrument panel, Figure 2-17,
Sheet 2. Pressing the switch while in the APR (NAV)
mode with the NAV CTL mode selector switch also
pressed, will cause the waypoint distance and bearing
to display on the pilot's HSI. This function will be
disabled if the FMS switch and/or the TACAN mode of
operation are selected.
(a) Pitch Hold Mode. Whenever a roll
mode is selected without a pitch mode, the ADI
command cue will display a pitch attitude hold
command. The pitch attitude can be changed by
pressing the TCS button on the control wheel and
maneuvering the aircraft. The command cue will be
synchronized to zero while the button is pressed.
Upon release of the button, the pitch command will be
such as to maintain the new pitch attitude. In the pitch
hold mode, the ADI command cue will be biased out of
view if the VG is not valid.
(b) TACAN Mode. The TACAN mode is
selected by pressing the DME/TAC alternate source
selector switch located on the pilot's radio control
panel. Annunciators, placarded TACAN/ADF 1, and
located on the instrument panel (both pilot and copilot
side) will illuminate. TACAN navigation information will
display on the pilot's HSI, and on the DME slave
The NAV/TAC receiver must be tuned to a
valid TACAN frequency.
TACAN functions are identical to VOR
using TACAN information rather than VOR
signals. The ARM/CAP annunciation is the
same as in VOR mode.
(4) Back Course Mode (BC). The back
course mode is selected by pressing the BC button on
the mode selector. Back course operates the same as
the LOC mode with the deviation and course signals
reversed to make a back course approach on the
localizer. When BC is selected, and outside the lateral
annunciators will illuminate. At the capture point, BC
CAP will be annunciated with BC ARM and HDG
annunciators extinguished. When BC is selected, the
glideslope circuits are locked out.
(5) Standby Mode (SBY ). The standby
mode is selected by pressing the SBY button on the
mode selector. This resets all the other flight director
modes and biases the ADI command cue from view.
While pressed, SBY acts as a lamp test causing all
mode annunciators to illuminate and the flight director
warning flag on the ADI to come in view. When the
button is released, the mode annunciator lights
extinguish and the flight director warning flag retracts
(6) Indicated Airspeed Hold Mode (IAS).
The indicated airspeed hold mode is selected by
pressing the IAS button on the mode selector. When
IAS is selected, it overrides the APR CAP, GA, ALT,
VS, and ALTSEL CAP modes. In the IAS mode the
pitch command is proportional to airspeed error
provided by the air data computer. Pressing and
holding the TCS button allows the pilot to maneuver
the aircraft to a new airspeed hold reference without
disengaging the mode. Once engaged in the IAS
mode, the mode will be reset if the air data computer is
not valid. The ADI command cue will bias out of view
if the VG is not valid.
(7) Vertical Speed Hold Mode (VS). The
vertical speed hold mode is selected by pressing the
VS button on the mode selector. When VS is
selected, it overrides the APR CAP, GA, ALT, ALTSEL
CAP, and IAS modes. In the VS mode, the pitch
command is proportional to VS error provided by the
air data computer. Pressing and holding the TCS
button allows the pilot to maneuver the aircraft to a
new vertical speed hold reference without disengaging
the mode. Once engaged in the VS mode, the mode
will be reset if the air data computer is not valid. The
ADI command cue will bias out of view if the VG is not