3-50 Change 3
21. YD ENGAGE push-button switch-indicator
(autopilot controller) - Depress while holding
rudder boost/yaw control test switch in TEST.
Yaw damper should not engage.
22. RUDDER BOOST/YAW CONTROL TEST
switch - RUDDER BOOST. Check RUDDER
BOOST annunciator extinguished.
23. Electric elevator trim - Check.
a. ELEV TRIM switch - ON.
b. Pilot and copilot trim switches - Check op-
Operation of the electric trim system should oc-
cur only by movement of pairs of switches. Any
movement of the elevator trim wheel while de-
pressing only one switch element indicates a
trim system malfunction. The electric elevator
trim control switch must then be turned OFF and
flight conducted by operating the elevator trim
wheel manually. Do no use autopilot.
c. Pilot and copilot trim switches - Check in-
dividual element for no movement of trim,
then check proper operation of both ele-
d. Pilot trim switches - Check that pilot
switches override copilot switches while
trimming in opposite directions, and trim
moves in the direction commanded by pi-
e. Pilot or copilot trim switches - Check trim
disconnects while activating pilot or copi-
lot trim disconnect switches.
f. ELEV TRIM switch - OFF then ON (ELEV
TRIM OFF annunciator extinguishes).
p. Digital Flight Control System Modes of Operation.
(1) Heading hold mode (wings level). The basic
lateral mode of the autopilot is heading hold. Heading
hold mode is defined as:
No lateral flight director mode selected
Bank angle less than 6 degrees
If the above conditions are satisfied, the autopilot will
roll the aircraft to a wings level attitude. When the air-
crafts bank angle is less than 3 degrees for 10 seconds,
the heading hold mode is automatically engaged. The
heading hold mode is not annunciated on the EADI as it
is the default lateral mode when no other lateral steering
mode is selected. Autopilot engagement is annunciated
on the EADI.
(2) Roll hold mode. The autopilot will recognize
the roll hold mode as being operational when:
No lateral flight director mode has been selected
The aircrafts bank angle is greater than 6 degrees,
but less than 35 degrees
The autopilot is engaged
When the above conditions have been satisfied, the
autopilot will maintain the desired bank angle. With the
autopilot engaged, bank angles up to 35 degrees can be
established using the turn knob. If touch control steering
(TCS) was used to initiate the roll, bank angles up to 35
degrees can be maintained and TCS ENG will be annun-
ciated on the EADI.
(3) Heading select mode. The heading select
mode is used to intercept and maintain a magnetic head-
ing. The mode is selected with the HDG switch-indicator
on the flight director mode selector panel (fig. 3-22).
Heading mode selection is annunciated by a green HDG
annunciator on the EADI. The heading marker is set on
the heading dial of the EHSI by means of the instrument
remote controller (pedestal extension, fig. 2-12). When
operating in the heading mode the flight control computer
provides inputs to the pitch and roll command cue on the
EADI to command a turn to the heading selected by the
heading marker located on the EHSI. Heading mode
signal gain is a function of airspeed. Bank angle limit is
25 degrees in the heading select mode.
Heading select mode is cancelled by:
Capture of any other lateral steering mode