SECTION IV. FUEL SYSTEM
2-32. FUEL SUPPLY SYSTEM.
The engine fuel supply system (Fig. 2-24) consists of two identical systems sharing a common fuel management
wing tanks, and a nacelle tank. Each auxiliary fuel system consists of one tank located between the nacelle and the
fuselage. A fuel transfer pump is located within each auxiliary tank. Additionally, the system has an engine-driven
boost pump, a standby fuel pump located within each nacelle tank, a fuel heater (engine oil-to-fuel heat exchanger
unit), a tank vent system, a tank vent heating system, and interconnecting wiring and plumbing. Total fuel tank
Engine operation using only the engine-driven primary (high-pressure) fuel pump without standby
pump or engine-driven boost pump fuel pressure is limited to 10 cumulative hours. This condition is
indicated by illumination of either the #1 or #2 FUEL PRESS warning annunciator and the simultane-
ous illumination of both MASTER WARNING annunciators. All time in this category shall be entered
on DA Form 2408-13-1 for the attention of maintenance personnel.
a. Engine Driven Boost Pumps.
A gear-driven boost pump, mounted on each engine supplies fuel under pressure to the inlet of the engine-driven
primary high-pressure pump for engine starting and all normal operations. Either the engine driven boost pump or
standby pump is capable of supplying suficient pressure to the engine-driven primary high-pressure pump and thus
maintain normal engine operation.
b. Standby Fuel Pumps. A submerged, electrically operated standby fuel pump, located within each nacelle
tank, serves as a backup unit for the engine-driven boost pump. The standby pumps are switched off during normal
system operations. A standby fuel pump will be operated during crossfeed operation to pump fuel from one system
to the opposite engine. The correct pump is automatically selected when the CROSSFEED switch is activated. Each
standby fuel pump has an inertia switch included in the power supply circuit. When subjected to a 5 to 6 g shock
loading, as in a crash situation, the inertia switch will remove electrical power from the standby fuel pumps. The
standby fuel pumps are protected by two 10-ampere circuit breakers placarded STANDBY PUMP #1 or #2 , located
on the overhead circuit breaker panel (Fig. 2-12), and four 5-ampere circuit breakers (two each in parallel) on the
hot battery bus.
c. Fuel Transfer Pumps. The auxiliary tank fuel transfer system automatically transfers the fuel from the aux-
iliary tank to the nacelle tank without pilot action. Motive low to a jet pump mounted in the auxiliary tank sump is
obtained from the engine fuel plumbing system downstream from the engine driven boost pump and routed through
the transfer control motive low valve. The motive low valve is energized to the open position by the control system
to transfer auxiliary fuel to the nacelle tank to be consumed by the engine during the initial portion of the light. When
an engine is started, pressure at the engine driven boost pump closes a pressure switch, which after a 30 to 50 sec-
ond time delay to avoid depletion of fuel pressure during starting, energizes the motive low valve. When auxiliary
fuel is depleted, a low-level loat switch de-energizes the motive low valve after a 30 to 60 second time delay. This
time delay function prevents cycling of the motive low valve due to sloshing fuel. If the motive low valve or the
associated control circuitry fails, the loss of motive low pressure when there is still fuel remaining in the auxiliary fuel
tank, is sensed by a pressure and loat switch which illuminates a caution annunciator placarded #1 NO FUEL XFR
or #2 NO FUEL XFR . During engine start, the pilot should note that the NO FUEL XFR annunciator extinguish 30
to 50 seconds after engine start. The NO FUEL XFR annunciator will not illuminate if auxiliary tanks are empty. A
manual override is incorporated as a backup for the automatic transfer system. This is initiated by placing the AUX
TRANSFER switch, located in the fuel management panel to the OVERRIDE position. This will energize the transfer
control motive low valve. The transfer systems are protected by 5ampere circuit breakers placarded AUXILIARY
TRANSFER #1 or #2 , located on the overhead circuit breaker panel (Fig. 2-12).