Attitude And Direction - Maintenance Practices; Horizon Gyro General Operation Notes; Attitude Indicator Removal/Installation - Cessna 172 Series 1996 Maintenance Manual

CESSNA AIRCRAFT COMPANY
MODEL 172
MAINTENANCE MANUAL
ATTITUDE AND DIRECTION - MAINTENANCE PRACTICES
1. General
A.
Three gyroscopic instruments that indicate attitude and direction, are mounted in the instrument panel.
Included are the attitude indicator, the directional gyro and the turn coordinator.
2. Precautions
A.
Gryoscopic instruments are very sensitive. They have precision bearings on the gyroscope rotor,
pivots, and the yoke shaft. Careless handling while the instrument is out of the aircraft, and dirt and
other contaminates can damage the bearings. Special precautions should be followed when handling,
installing, removing, or shipping any gyroscopic instruments.
(1)
During removal of instruments, place cushioning material between the instruments and the
control column.
(2)
Do not vibrate or shake panel or instruments.
(3)
Do not drop, shake, place on hard surface, or bump gyroscope against any other object.
(4)
Do not remove any wires, labels, tie straps, or any parts original to the gyro.
(5)
Visually check the gyro for any external damage. There should be no scratches, dents, or dings
on any part of the gyro. Do not install any gyros that have scratches, dents, or dings.
(6) Any instruments that are to be shipped, should have all female ports plugged with removable
port plugs, and all male receptacles capped with removable plastic caps.
(7)
Pack all gyros in styrofoam or other cushioning material for storage and transportation. When
shipping gyroscope pack in original box if possible.
(8)
Shipping plugs should be kept in the air ports except when the instrument is installed in an aircraft
or being tested.
3.
Horizon Gyro General Operation Notes
A.
The horizon gyro (attitude) is an instrument that requires air flow to move the gyro rotor for normal
operation. The airflow is provided by the vacuum system. Any abnormalities (vacuum system or
other) that effect the function and movement of the gyro rotor, can effect indicating accuracy and
performance.
B.
The horizon gyro requires approximately 4.5 to 5.5 inches Hg to adequately spin the rotor. The gyro
reaches rated performance in a minimum of 3 minutes of rotor spin time with rated vacuum applied.
C.
The gyro rotor may continue to spin for approximately 15 minutes after air to the system is removed.
While the rotor is spinning down, it will normally start to show a change in the roll and/or pitch indication,
and when completely stopped will remain in a roll and/or pitch indication until the system is started
again.
D.
If a gyro has been shut down and started again before the rotor has been allowed to stop, it requires
considerably more time to erect to the correct pitch and roll indication.
4.
Attitude Indicator Removal/Installation
A.
Remove Attitude Indicator (Refer to Figure 201).
(1) Gain access to the back of the attitude indicator by removing screws securing flight instrument
sub-panel to instrument panel.
(2)
Disconnect vacuum hoses and electrical connector from attitude indicator.
(3) Remove screws securing attitude indicator to flight instrument sub-panel.
(4) Remove attitude indicator.
B.
Install Attitude Indicator (Refer to Figure 201).
(1)
Position attitude indicator on flight instrument sub-panel and secure with screws.
(2)
Connect vacuum hoses and electrical connector to attitude indicator.
(3) Secure flight instrument sub-panel to instrument panel with screws.
34-20-00 Page 201
Aug 18/2001