Table of Contents
Advertisement
AUXILIARY FUEL PUMP
SWITCHING SYSTEM
SUPPLEMENTAL
AIRPLANE FLIGHT MANUAL
SECTION 1
GENERAL
AUXILIARY FUEL PUMP SWITCHING SYSTEM
To improve the reliability of the auxiliary fuel pump systems in Cessna
conventional twin-engine airplanes (except Model 310 airplanes prior to Model
310C which are not affected by this change), the automatic fuel pressure sensing
switch and auxiliary fuel pump switch for each engine have been removed and
replaced with new three-position, lever lock, toggle-type auxiliary fuel pump
switches and circuitry. This modification provides direct pilot control of the
output pressure of the two auxiliary fuel pumps. The switches are labeled AUX
PUMP, L (left engine) and R (right engine) and switch positions are LOW, OFF,
and HIGH. The LOW position operates the auxiliary pumps at low speed and
can be used, when required, to provide supplementary fuel pressure for all normal
operations. The switches are OFF in the middle position. The HIGH position is
reserved for emergency operation, and operates the pumps at high speed. The
HIGH position supplies sufficient fuel flow to sustain partial engine power in the
event of an engine-driven fuel pump failure. The switches are locked out of the
HIGH position and the switch toggle must be pulled out
to
clear a detent before
it can be moved to the HIGH setting. The toggle need not be pulled to return the
switch
to
OFF.
In Models 340A, 414, 421, 421A and 421B, additional fuel tank selector logic
is added to activate the auxiliary fuel tank system in-line fuel pumps when the
auxiliary fuel tanks are selected, thereby making the auxiliary tank in-line pump
operation independent of the auxiliary fuel pump switches.
SWITCH OPERATION
Operation of the new switching system is simple and straightforward. The
new LOW position of the auxiliary fuel pump switches should be used whenever
an original manual/handbook or checklist procedure specifies either LOW
(PRIME in early 310 or 320 airplanes) or ON. The LOW position is also used
anytime there are indications of vapor, as evidenced by a "nervous" fuel flow
needle. Auxiliary fuel pumps, if needed, are
to
be operated on LOW in all
conditions except when an engine-driven fuel pump fails.
The new HIGH position supplies sufficient fuel flow to sustain partial engine
power and should be used solely to sustain the operation of an engine in the
event its engine-driven fuel pump fails. Failure of an engine-driven fuel pump will
be evidenced by a sudden reduction in the fuel flow indication immediately
prior to a loss of power while operating from a fuel tank containing adequate
fuel.
In
an emergency where loss of an engine:driven fuel pump is involved, pull
out on the applicable auxiliary fuel pump switch to clear the detent and select the
HIGH position. Then adjust the throttle and mixture controls to obtain sat-
2
Original Issue
Advertisement
Table of Contents
