Cessna 150M - Trouble Shooting-Pitot Tube Heater; Pitot Tube Alignment; Vacuum System

15-21. TROUBLE SHOOTING--VERTICAL SPEED INDICATOR. (Cont)
TROUBLE PROBABLE CAUSE REMEDY
POINTER OSCILLATES.
(cont).
Leak in static line.
Test lines and connections for
leaks.
Repair or replace dam-
aged lines, tighten connections.
Leak in instrument case. Substitute known-good indicator
and check reading. Replace
instrument.
HAND VIBRATES. Excessive vibration.
Check shock mounts. Replace
defective shock mounts.
Defective diaphragm.
Substitute known-good indicator
and check for vibration. Re-
place instrument.
15-22. TROUBLE SHOOTING--PITOT TUBE HEATER.
TROUBLE PROBABLE CAUSE REMEDY
TUBE DOES NOT HEAT OR Switch turned "OFF."
Turn switch "ON. "
CLEAR ICE.
Blown fuse. Check fuse.
Replace fuse.
Break in wiring.
Test for open circuit.
Repair
wiring.
Heating element burned out.
Check resistance of heating
15-23. PITOT TUBE ALIGNMENT. (Refer to fig-
ure 15-2.) For correct airspeed indication pitot
tube (18) must be properly aligned. Open end of tube
must be perpendicular to longitudinal axis of aircraft.
A template like the one shown in figure 15-4 will
prove the most convenient means of checking align-
ment. Prior to using template, check that pitot tube
parallels row of rivets just outboard of tube. A
straightedge may be placed along row of rivets to
check the alignment. The template fits over the wing
leading edge and should conform to the illustration.
the illustration has been drawn carefully to actual
size and may be traced directly on a piece of carbon
paper between the printed page and the template ma-
terial, then trace contours.
15-24. VACUUM SYSTEM. (Refer to figure 15-5.)
element. Replace element.
15-25. DESCRIPTION. Suction to operate the gyros
is provided by a dry-type engine-driven vacuum
pump, gear-driven through a spline-type coupling.
A
suction relief valve, to control system pressure,
is connected between the pump inlet and the instru-
ments. In the cabin, the vacuum line is routed from
gyro instruments to the relief valve at the firewall.
A central air filtering system is utilized. Beginning I
with aircraft serial 15075525 and A1500480 a throw
away type air filtering unit is installed. The unit is
installed with sta-straps for quick change capability.
The reading of the suction gage indicates net differ-
ence in suction before and after air passes through a
gyro. This differential pressure will gradually de-
crease as the central aii' filter becomes dirty, caus-
ing a lower reading on the suction gage.
Change 2 15-9