THE NEW PIPER AIRCRAFT, INC.
PA-32-301FT / 301XTC
MAINTENANCE MANUAL
PAGE 3
Feb 19/04
3I3
34-20-00
4. Directional Gyro
A. Description
Directional gyro is a flight instrument incorporating an air driven gyro stabilized in vertical plane.
Gyro is rotated at high speed by lowering pressure in air tight case and simultaneously allowing
atmospheric air pressure to enter instrument against gyro buckets. Due to gyroscopic inertia, spin
axis continues to point in same direction even though aircraft yaws to right or left. This relative
motion between gyro and instrument case is shown on instrument dial which is similar to a
compass card. Dial, when set to agree with airplane magnetic compass, provides a positive
indication free from swing and turning error. However, directional gyro has no sense of direction and
must be set to magnetic compass. Since magnetic compass is subject to errors due to magnetic
fields, electric instruments, etc, directional gyro is only accurate for heading it has been set for. If
gyro is set on 270°, for instance, and aircraft is turned to some other heading, there can be a large
error between gyro and magnetic compass due to error in compass compensation. This will appear
as gyro precession. Gyro should only be checked to heading on which it was first set. Due to
internal friction, spin axis error, air turbulence and airflow, gyro should be set at least every 15
minutes for accurate operation, whether it has drifted or not.
B. Troubleshooting
See Chart 2.
CHART 2
TROUBLESHOOTING DIRECTIONAL GYRO
Trouble Cause Remedy
Excess drift in either Setting error. Review paragraph titled
direction. “Description” for gyro
operation.
Defective instrument. Replace instrument.
High or low vacuum. If vacuum
is not correct, check for the
following:
1. Relief valve improperly 1. Adjust relief valve
adjusted.
2. Incorrect gauge reading. 2. Replace gauge.
3. Pump failure. 3. Repair or replace.
4. Vacuum line kinked or 4. Check and repair. Check
leaking. for collapsed inner wall
of hose.
Dial spins during turn. Limits (55° bank) of gimbal Recage gyro in level flight.
exceeded.
Dial spins continuously. Defective mechanism Replace.
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