Piper COMANCHE PA-24-180 Service Manual page 671

PIPER COMANCHE SERVICE MANUAL
11-38. Airpeed Indicaor.
1-39 Genera. The airspeed indicator provides a means of indicaing the speed of the airplane pasing
through the air. The airspeed indication is the differential pressure reading between pirot air pressure and
sttic air pressure. Ths instrument ha the diphragm vented to the pitot ar source and the case s vented
to the static air svysem. As the airplane increases speed. the pitor air pressure increases. cusing the
diaphragm to exrand. A mechanimca 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 necessarv
operating range markings for safe operation of the airplane.
11-40 Removal And Replacement. Refer to Paragraph 11-18 of this section.
11-41. Troubleshooting.
TABLE XI-VI. AIRSPEED TUBES AND INDICATOR
Trouble Cause
Remedy
Tube does not heat or
dear itelf of ice with
switch "ON" (Heated
pilro tubes only.)
Tube does not heat or
clear itself of ice with
switch "ON" (Heated
pitot rubes only )
Circuit breaker popped.
Open circuit.
Reset.
Repair.
Excessive voltage drop
between barrerv and
pitot head.
Heating element burned out.
Check voltage at pitot
head.
Replace pitot head.
Pointers of static inmsu-
menrs do not indicate
oroperly
Pointer of instrument
oscillates.
Leak in nstrument case or
in plot lines.
Leak in Instrument case.
Check for leak and seal
Check for leak and seal
INSTRUMENTS
ISSUED: 8/18/72
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