Cessna 150M - Instruments; Pitot and Static Systems; Statis Pressure System Inspection and Leakage Test; Removal

15-3. INSTRUMENT PANEL. (Refer to figure 15-1.)
15-4. DESCRIPTION. The instrument panel assem-
bly consists of a stationary and shock-mounted panel.
The stationary panel contains fuel and engine instru-
ments, which are NOT sensitive to vibration. The
shock-mounted panel contains major flight instru-
ments such as horizontal and directional gyros which
ARE affected by vibration. Most of the instruments
are screw-mounted on the panel backs.
15-5. REMOVAL AND INSTALLATION. The sta-
tionary panel is secured to engine mount stringers
and a forward fuselage bulkhead and ordinarily is not
considered removable. The shock-mounted panel is
secured to stationary panel with rubber shock-mount-
ed assemblies. To remove shock-mounted panel
proceed as follows:
a. Unscrew threaded buttons securing decorative
cover to panel and remove cover.
b. Remove nuts from shock-mounts, tag and dis-
connect instrument wiring and plumbing and pull panel
straight back.
c. Reverse preceding steps for installation. En-
sure ground strap is properly installed.
15-6. SHOCK MOUNTS. Service life of instruments
is directly related to adequate shock-mounting of
panel. If removal of panel is necessary, check
mounts for deterioration.
15-7. INSTRUMENTS. (Refer to figure 15-1.)
15-8. REMOVAL. Most instruments are secured
to panel with screws inserted through panel face.
To remove an instrument, remove decorative cover,
disconnect wiring or plumbing to instrument, re-
move mounting screws and take instrument out from
behind, or in some cases, from front of panel. In-
strument clusters are installed as units and are
secured by a screw at each end. A cluster must be
removed from panel to replace an individual gage.
NOTE
Thru 1975 models the clusters are located
directly above the glove box. Removal of
the cluster will be simpler if the glove box
is removed first. Beginning with 1976
models, the instrument cluster is located
below the pilots control column.
In all cases when an instrument is removed, dis-
connected lines or wires should be protected. Cap
open lines and cover pressure connections on in-
strument to prevent thread damage and entrance of
foreign matter. Wire terminals should be insulated
or tied up so accidental grounding or short-circuiting
will not occur.
15-9. INSTALLATION. Generally, installation pro-
cedure is the reverse of removal procedure. Ensure
mounting screw nuts are tightened firmly, but do not
over-tighten, particularly on instruments having
plastic cases. The same rule applies to connecting
plumbing and wiring.
NOTE
All instruments (gages and indicators), re-
quiring a thread seal or lubricant, shall be
installed using teflon tape on male fittings
only. This tape is available through Cessna
Service Parts Center.
When replacing an electrical gage in an instrument
cluster assembly, avoid bending pointer or dial
plate. Distortion of dial or back plate could change
calibration of gages.
15-10. PITOT AND STATIC SYSTEMS. (Refer to
figure 15-2.)
15-11. DESCRIPTION. The pitot system conveys
ram air pressure to the airspeed indicator. The
static system vents vertical speed indicator, alti-
meter and airspeed indicator to atmospheric pres-
sure through plastic tubing connected to a static port.
A static line sump is installed at source button to
collect condensation in static system. A pitot tube
heater may be installed. The heating element is con-
trolled by a switch at instrument panel and powered
by the electrical system.
15-12. MAINTENANCE. Proper maintenance of
pitot and static system is essential for proper opera-
tion of altimeter, vertical speed and airspeed indi-
cators. Leaks, moisture and obstructions in pitot
system will result in false airspeed indications,
while static system malfunctions will affect readings
of all three instruments. Under instrument flight
conditions, these instrument errors could be hazar-
dous. Cleanliness and security are the principal
rules for system maintenance. The pitot tube and
static ports MUST be kept clean and unobstructed.
15-13. STATIC PRESSURE SYSTEM INSPECTION
AND LEAKAGE TEST. The following procedure
outlines inspection and testing of static pressure
system, assuming altimeter has been tested and in-
spected in accordance with current Federal Aviation
Regulations.
a. Ensure static system is free from entrapped
moisture and restrictions.
b. Ensure no alterations or deformations of air-
frame surface have been made which would affect
the relationship between air pressure in static pres-
sure system and true ambient static air pressure for
any flight configuration.
c. Attach a source of suction to static pressure
source opening. Figure 15-3 shows one method of
obtaining suction.
d. Slowly apply suction until altimeter indicates a
1000-foot increase in altitude.
When applying or releaSing suction, do not
exceed range of vertical speed indicator or
airspeed indicator.
Change 3 15-3