Piper PA-28-161, Maintenance Manual

Page: 569 / 1104

PIPER AIRCRAFT, INC.
PA-28-161, WARRIOR III
MAINTENANCE MANUAL
PAGE 1
Nov 30/06 3H1
34-20-00
ATTITUDE AND DIRECTION
1. Attitude Deviation Indicator (ADI) / Artificial Horizon
NOTE: For airplanes equipped with the Avidyne Entegra EFIS, the primary attitude indicator is the
Primary Flight Display (PFD).
A. Description and Operation
CAUTION: THE GYRO AIR FILTER MUST BE CLEAN OR REPLACED BEFORE ADJUSTING
GYRO AIR PRESSURE.
The ADI/Artificial Horizon is essentially an air driven gyroscope rotating in a horizontal plane and is
operated by air flow directed at gyro buckets causing the rotor to spin approximately 17,000 to
22,000 rpm. Gyroscopic inertia causes the gyroscope to remain relatively rigid in space. The
instrument case moves freely about the spinning gyro rotor in three dimensions due to a gimbal
assembly. An attitude bar across the face of the indicator represents the horizon and aligning the
miniature airplane to the attitude bar simulates the alignment of the airplane to the actual horizon.
Any deviation simulates the deviation of the airplane from the true horizon. The ADI is marked for
different degrees of bank. The display is stable and shows minute attitude changes of as little as
one degree. A rapidly wobbling and leveling pitch bar, when vacuum is first applied, is normal and
indicates the erection mechanism in action. The instrument can be adjusted for parallax by a knob
on the lower center instrument face.
The gyro is driven primarily by the engine driven dry pneumatic vacuum pump. As an option, an
electrically operated vacuum pump can be installed as a backup in the event of primary pump
failure. Air volume, not air pressure, spins the gyro rotor. A pressure regulator will automatically
adjust air pressure within proper limits. If the air filter becomes contaminated, restricting air flow,
gyro rotor speed will be reduced.
B. Troubleshooting
See Chart 1.
Service is restricted to instrument installation and power source. Obvious malfunctions require
repair or replacement. Typical installation induced malfunctions are due to restricted air flow from air
line kinks or leaks, contaminated air filters, deteriorating electrical grounds, sagging instrument
panel shock mounts, system regulators, faulty vacuum/pressure gauges. (Air pressure must be 5.5
plus or minus 0.5 in. Hg). Replace or repair the instrument only after the operating system has
proven to be good.