Cessna 402C - Page 235

G~"402C
MODEL
PilOT PRESSURE SYSTEM
SECTION 7
AIRPLANE & SYSTEMS DESCRIPTIONS
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The standard pitot pressure system, see Figure 7-21. consists of an
electrically heated pitot tUbe mounted on the left side of the fuselage aft
of the nose cap, suitable plumbing and an airspeed indicator.
When the pitot heat switch is placed in the ON position. the heating
elements ;n the pitot tube are electrically heated to maintain proper
operation of the system during icing conditions. Do not operate for pro-
longed periods while on the ground to prevent overheating of the heating
elements.
When the optional copilot' 5 instruments are installed, a second pitot
system i~ used. This second pitot head is located on the right side of the
fuselage aft of the nose cap and is connected to the copilot ' s airspeed
indicator. This dual system allows a completely independent second presen-
tation of airspeed pitot pressure. Pitot heat for the additional head iSI
controlled by the standard pitot heat switch.
STATIC PRESSURE SYSTEM
Static pressure for the pilot's airspeed, altimeter and rate-of-climb
indicators, see Figure 7-20, is obtained by a nonnal external static source
or an alternate internal static source should the external source fail.
An alternate static source, installed in the static system directly
below the parking brake handle, supplies an alternate static source to the
pilot's instruments should the external static source malfunction. Refer
to Section 5 for airspeed and altimeter corrections when the alternate
static source is used. A drain valve is located behind the map pocket on
the copilot
1
s side.
When the optional copilot
'
s
instruments are installed, a second set of
static ports are installed aft of the main cabin door below the standard
static ports. The added static ports are manifol ded together and are used
as a reference for the copilot's instruments only. This dual system allows
a camp 1 etel y independent second sta tic pressu re SOurce. No a lterna te
static source is provided for the copilot's instruments. Optional static
port heaters are controlled by the stall and vent heat switch.
VACUUM SYSTEM
A vacuum system, see Figure 7-22, is installed to provide a source of
vacuum for the vacuum instruments. The system consists of an engine-driven
vacuum pump on each engine, pressure rel ief val ve for each pump, a common
vacuum manifold, vacuum air filter, suction gage and gyro instruments.
Each vacuum pump pull s a vacuum on the common manifold, exhausting the
air overboard. The maximum amount of vacuum pulled o~ the manifold by each
vacuum pump is controlled to a preset level by each pressure rel ief valve.
Should either of the pumps fail, a check valve is provided in each end of
the manifold to isolate the inoperative vacuum pump from the system.
1
November 1979
Revision 4 - 1
December 1983
7-31