Piper Aircraft Corporation Malibu Mirage PA-46-350P, Airplane Maintenance Manual

Page: 951 / 1956

PAGE 5
Feb 28/07 5D9
34-20-00
PIPER AIRCRAFT, INC.
PA-46-350P, MALIBU MIRAGE
MAINTENANCE MANUAL
4. Air Driven Heading Indicator (i.e. - Directional Gyro)
The air driven heading indicator is offered as an option for the copilots navigation instrument package.
The air driven heading indicator is a flight instrument incorporating an air driven gyro stabilized in the
vertical plane. The gyro is rotated at high speed by lowering the pressure in the air tight case and
simultaneously allowing atmospheric air pressure to enter the instrument against the gyro buckets. Due
to gyroscopic inertia, the spin axis continues to point in the same direction, even though the aircraft yaws
to the right or left. This relative motion between the gyro and the instrument case is shown on the
instrument dial, which is equipped with a 360° compass card. The card, when set to agree with the
airplane's magnetic compass, provides a positive indication free from acceleration/deceleration and
turning errors. However, the heading indicator has no sense of direction, and must be set to the
magnetic compass. Since the magnetic compass is subject to errors due to magnetic fields, electric
instruments, etc, the directional gyro is only accurate for the heading it has been set for. If the gyro is set
on 270°, for instance, and the aircraft is turned to some other heading, there can be a large error
between the gyro and the magnetic compass due to the error in compass compensation. This will appear
as gyro precession. The gyro should frequently be checked precession. Due to internal friction, span axis
error, air turbulence and airflow, the gyro should be set at least every 15 minutes for accurate operation,
whether it has drifted or not.
A. Troubleshooting
See Chart 4.
B. Removal and Installation
See 39-10-00, Face Mounted Instruments - Removal and Installation.
CHART 4
TROUBLESHOOTING AIR DRIVEN HEADING INDICATOR
Trouble Cause Remedy
Excess drift in either Setting error. Review Directional Gyro (4).
direction.
Defective instrument. Replace instrument.
High or low vacuum. If
vacuum is not correct,
check for the following:
1. Relief valve improperly 1. Adjust.
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.