General; Troubleshooting - Piper SENECA II Service Manual

10-35. AIRSPEED INDICATOR.

10-36. GENERAL.

The airspeed indicator provides a means of indicating the speed of the airplane passing through the air.
The airspeed indication depends on the differential pressure between pitot air pressure and static air
pressure. This instrument has the diaphragm vented to the pitot air source and the case is vented to the
static air system. As the airplane increases speed, the pitot air pressure increases, causing the diaphragm
to expand. A mechanical linkage picks up this motion and moves the instrument pointer to the indicated
speed. The instrument dial is calibrated in knots and miles per hour, and also has the necessary operating
range markings for safe operation of the airplane.

10-37. TROUBLESHOOTING.

Trouble
Pointers of static
instruments do not
indicate properly.
Pointer of instrument
oscillates.
Instrument reads high.
Instrument reads low.
Airspeed changes as
aircraft is banked.
NOTE: If any connections in the pitot / static system are opened for maintenance, the entire system
must be rechecked per Pitot / Static System, Test, above.
10-38. REMOVAL AND REPLACEMENT. Refer to Paragraph 10-72 of this section.
01/01/09
PIPER SENECA II SERVICE MANUAL
TABLE X-VI. AIRSPEED TUBES AND INDICATOR
Leak in instrument case
or in static lines.
Defective mechanism.
Pointer not on zero.
Leaking static system.
Pointer not on zero.
Leaking static system.
Pitot-Static head not
aligned correctly.
Water in static line.
Cause
2F1
Remedy
Check for leak and seal.
Replace instrument.
Replace instrument.
Find leak and correct.
Replace instrument.
Find leak and correct.
Realign pitot-static head
Remove lines from static
instruments and blow
out lines from cockpit
to pitot-static head.
X - INSTRUMENTS