PIPER SENECA II SERVICE MANUAL
01/01/09 X - INSTRUMENTS
2F1
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.
TABLE X-VI. AIRSPEED TUBES AND INDICATOR
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.
Trouble Cause Remedy
Pointers of static Leak in instrument case Check for leak and seal.
instruments do not or in static lines.
indicate properly.
Pointer of instrument Defective mechanism. Replace instrument.
oscillates.
Instrument reads high. Pointer not on zero. Replace instrument.
Leaking static system. Find leak and correct.
Instrument reads low. Pointer not on zero. Replace instrument.
Leaking static system. Find leak and correct.
Pitot-Static head not Realign pitot-static head
aligned correctly.
Airspeed changes as Water in static line. Remove lines from static
aircraft is banked. instruments and blow
out lines from cockpit
to pitot-static head.
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