4. Airspeed Indicator
NOTE: For airplanes equipped with the Avidyne Entegra EFIS, the primary airspeed indicator is the
Primary Flight Display (PFD).
A. Description and Operation
The airspeed indicator reads the speed of the airplane passing through the air. Airspeed indication
is the differential pressure reading between pitot air pressure and static air pressure. The instrument
has the diaphragm vented to the pitot air source. The case is vented to static air system. As airplane
speed increases, pitot air pressure increases, causing diaphragm to expand. A mechanical linkage
moves the pointer to show speed. The instrument dial is calibrated in knots and miles per hour, and
has operating range markings for safe operation of the airplane.
B. Troubleshooting
See Chart 3.
NO
TE: If any connections in static system are opened for maintenance, the complete system must
be rechecked per F.A.R. 23.1325.
PIPER AIRCRAFT, INC.
PA-28-161, WARRIOR III
MAINTENANCE MANUAL
PAGE 6
Nov 30/06
3G14
34-10-00
CHART 3
TROUBLESHOOTING AIRSPEED INDICATOR AND LINES
Trouble Cause Remedy
Pointers of stick instruments Leak in instrument case or Check for leak and seal.
do not indicate properly. in pitot lines.
Pointer of instrument Defective mechanism. Replace instrument.
oscillates.
Instrument reads high. Pointer not on zero. Replace instrument.
In Flight: Leaking static system. Find leak and correct.
On Ground: Leaking pitot system. Find leak and correct.
Instrument reads low. Pointer not on zero. Replace instrument.
In Flight: Leaking pitot system. Find leak and correct.
On Ground: Leaking static system. Find leak and correct.
Airspeed changes as aircraft Pitot head not aligned. Align pitot head.
is banked.
Water in pitot line. Remove lines from static
instruments and blow out
lines from cockpit to pitot
head.
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