Directional Gyro Check .
Directional Gyro Operational Check
NOTE: The permitted limit for gyro drift on the ground or in flight is 4 degrees from a fixed heading, during a 10-minute period.
(1) Start the airplane engine.
(2) Make sure that the vacuum system operates correctly.
(a) The vacuum gage must show between 4.5 and 5.5 inches Hg.
(3) Let the directional gyro become stable for at least 3 minutes.
(4) If the directional gyro dial starts to turn, let the gyro become stable and then push the gyro-caging knob. If the gyro dial continues to turn, repair the system and/or replace the gyro.
NOTE: It is usual for the directional gyro dial to turn when the gyro becomes stable. This is not
a cause for removal.
(5) Point the airplane's heading to the north.
(6) Set the directional gyro to the north.
(7) Make sure that the DG dial drift is not more than 4 degrees in a 10-minute period.
(8) Do steps 5 through 7 again for each cardinal heading (North, West, South, and East).
(9) If the directional gyro dial drift is not satisfactory at any heading, repair the system and/or replace the gyro.
NOTE: After stop operation of the airplane, it is usual for the directional gyro dial to continue to turn. This is not a cause to remove the gyro.
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