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CESSNA AIRCRAFT COMPANY
MODEL 172
MAINTENANCE MANUAL
AUTOPILOT - MAINTENANCE PRACTICES
1.
General
A.
A single axis autopilot featuring heading hold is installed on IFR equipped airplanes. Heading hold is
based on directional gyro input and can incorporate VOR, GPS or Localizer input on demand.
B.
A dual axis autopilot is available as an option. The two axis system provides both vertical speed and
altitude hold selection. Altitude alerting and altitude preselection are optional features with the two
axis autopilot system.
2.
Roll Servo Removal/Installation
A.
Remove Roll Servo (Refer to Figure 201).
(1) Remove access panel 620AB. Refer to Chapter 6, Access/Inspection Plates - Description and
Operation.
(2) Loosen roll servo cable turnbuckle.
(3) Disconnect electrical connector from roll servo.
(4) Remove cable guard and cable.
(5) Remove screws securing roll servo to bracket.
(6) Remove roll servo from airplane.
B.
Install Roll Servo (Refer to Figure 201).
(1) Position roll servo to bracket and secure with screws.
(2) Connect electrical connector to roll servo.
NOTE:
Removal of servo mount requires disconnecting the servo cable. Consequently, servo
cable rigging is required upon reinstallation of the servo mount.
(3) Install roll servo cable on roll servo.
NOTE:
System rigging should be accomplished with aileron and bellcrank in neutral position.
NOTE:
Wrap cable around servo drum approximately 1.25 turns each direction from swaged
ball (drum ball detent facing inboard).
NOTE:
When installing cable guard, ensure that the legs of the cable guard do not touch the
cable. Be sure that feet of cable guard straddle notches around perimeter of mount.
(4)
Adjust roll servo cable tension with turnbuckle to obtain cable tension of 15 pounds, ±3 pounds
(66.7 N, ±13.34 N).
(5) Turn power ON to autopilot controller.
(6) Move heading bug on directional gyro left and right of current heading to verify proper deflection
of ailerons.
3.
Pitch Servo Removal/Installation
A.
Remove Pitch Servo (Refer to Figure 201).
(1) Remove access plates 31 OAR, 340AL and 340AR. Refer to Chapter 6, Access/Inspection Plates
- Description and Operation.
(2) Disconnect electrical connector from pitch servo.
(3) Release cable tension, loosen pitch servo cable at turnbuckle.
(4) Remove cable guard and cable.
(5) Remove bolts securing pitch servo to bracket assembly.
(6) Remove pitch servo from airplane.
B.
Install Pitch Servo (Refer to Figure 201).
(1) Position pitch servo to bracket assembly in the install position and secure with bolts.
22-10-00
Page 201
Aug 18/2001
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Troubleshooting
