Cessna 150M - True Airspeed Indicator

15-17. TROUBLE SHOOTING--PITOT STATIC SYSTEM.
TROUBLE
PROBABLE CAUSE
REMEDY
LOW OR SLUGGISH AIRSPEED
Pitot tube obstructed, leak or
Test pitot tube and line for leaks
INDICA TION.
(N ormal altimeter
obstruction in pitot line.
or obstructions.
Blowout tube
and vertical speed. )
and line, repair or replace dam-
aged line.
INCORREC T OR SLUGGISH
Leaks or obstruction in static
Test line for leaks and obstruc-
RESPONSE. (all three
line.
tions.
Repair or replace line,
instruments. )
blowout obstructed line.
15-18. TRUE AIRSPEED INDICATOR. A true air-
speed indicator may be installed. This indicator,
equipped with a conversion ring, may be rotated until
pressure altitude is aligned with outside air tempera-
ture, then airspeed indicated on the instrument is read
as true airspeed on the adjustable ring. Refer to fig-
ure 15-2 for removal and installation. Upon installa-
tion, before tightening mounting screws (6), calibrate
instrument as follows: Rotate ring (8) until 120 mph
60°F aligns with zero pressure altitude, then tighten
mounting screws (6) and replace decorative cover (5).
NOTE
on
the adjustable ring aligns with 120 mph on the in-
dicator. Holding this setting, move retainer (7) until
Beginning with 1976 models, true airspeed
indicators are graduated in knots. There-
fore, on these aircraft, use 105K instead
of 120MPH in the above calibration procedure.
15-19. TROUBLE SHOOTING--AIRSPEED INDICATOR.
TROUBLE
PROBABLE CAUSE
REMEDY
HAND FAILS TO RESPOND. Pitot pressure connection not
Test line and connection for leaks.
properly connected to pres-
Repair or replace damaged line,
sure line from pitot tube.
tighten connections.
Pitot or static lines clogged.
Check line for obstructions. Blow
out
lines.
INCORRECT INDICATION
Leak in pitot or static lines.
Test lines and connections for
OR HAND OSCILLATES.
leaks.
Repair or replace dam-
aged lines, tighten connections.
Defective mechanism or
Substitute known-good indicator
leaking diaphragm.
and check reading.
Replace
instrument.
HAND VIBRATES.
Excessive vibration.
Check panel shock mounts.
Re-
place defective shock mounts.
Excessive tubing vibration.
Check clamps and line connections
for security. Tighten clamps and
connections, replace tubing with
flexible hose.
15-6 Change 3