Cockpit Reference Guide

Garmin G1000 Cockpit Reference Guide for the Cessna Nav III
190-00384-08 Rev. A
SECTION 6 – AUTOMATIC
FLIGHT CONTROL
6-22
6.4 AUTOPILOT OPERATION
NOTE: Refer to the AFM for specific instructions
regarding emergency procedures.
Cessna Nav III’s autopilot operates flight control
surface servos to provide automatic flight control. The
autopilot controls the aircraft pitch and roll attitudes
following commands received from the flight director.
Pitch autotrim provides trim commands to the pitch trim
adapter to relieve any sustained effort required by the
pitch servo.
Flight Control
Pitch and roll commands are provided to the servos,
based on the active flight director modes. Servo motor
control limits the maximum servo speed and torque. The
servo gearboxes are equipped with slip-clutches set to
certain values. This allows the servos to be overridden in
case of an emergency.
Pitch Axis and Pitch Trim
The autopilot pitch axis uses pitch rate to stabilize the
aircraft pitch attitude during upsets and flight director
maneuvers. Flight director pitch commands are rate- and
attitude-limited, combined with pitch damper control, and
sent to the pitch servo motor. The pitch servo measures
the output effort (torque) and provides this signal to the
pitch trim servo. The pitch trim servo commands the
motor to reduce the average pitch servo effort.
When the autopilot is not engaged, the pitch trim servo
may be used to provide manual electric trim. This allows
the aircraft to be trimmed using a control stick switch
rather than the trim wheel. Manual trim commands are
generated with the MET Switch. Trim speeds are scheduled
with airspeed to provide more consistent response.
Roll Axis
The autopilot roll axis uses roll rate to stabilize aircraft
roll attitude during upsets and flight director maneuvers.
The flight director roll commands are rate- and attitude-
limited, combined with roll damper control, and sent to
the roll servo motor.
Engaging the Autopilot
NOTE: Autopilot engagement/disengagement is
not equivalent to servo engagement/disengage-
ment. Use the CWS Button to disengage the
pitch and roll servos while the autopilot remains
active.
When the AP Key is pressed, the autopilot and flight
director (if not already engaged) are activated. Engagement
is indicated by a green ‘AP’ annunciation in the center of
the AFCS Status Box. The flight director engages in Pitch
and Roll Hold modes when initially activated.
Figure 6-26 Autopilot Engaged
Autopilot Engaged