entrance door, hold a fuel-proof container under the
ends, and drain about a pint of fuel out of each line.
i. Fuel Drain Collector System C D . Each
engine is provided with a fuel drain collector system to
return fuel, dumped from the engine during clearing
and shutdown operations, back into its respective
nacelle tank. The system draws power from the 4
feeder bus and fuel transfer is completely automatic.
Fuel from the engine flow divider drains into a collector
tank mounted below the aft engine accessory section.
An internal float switch actuates an electric scavenger
pump, which delivers the fuel to the fuel purge line just
aft of the fuel purge shutoff valve. A check valve in the
line prevents the backflow of fuel during engine
purging. The circuit breaker for both pumps is located
in the fuel section of the overhead circuit breaker
panel, placarded SCAVENGER PUMP. A vent line,
plumbed from the top of the collector tank, is routed
through an inline flame arrester and then downward to
a drain manifold on the underside of the nacelle.
j. Fuel Purge System T . Each engine is
provided with a fuel purge system. The system is
designed to ensure that any residual fuel in the fuel
manifolds is consumed during engine shutdown.
During engine operation, compressor discharge air is
routed through a filter and check valve, pressurizing a
small air tank mounted on the engine truss mount.
During engine shutdown, the pressure differential
between the air tank and fuel manifolds causes air to
be discharged from the air tank through a check valve
and into manifolds out through the nozzles and into the
combustion chamber. The fuel forced into the
momentary rise in engine speed.
k. Fuel Vent System. Each fuel system is
vented through two ram vents located on the
underside of the wing adjacent to the nacelle. To
prevent icing of the vent system, one vent is recessed
into the wing and the backup vent protrudes out from
the wing and contains a heating element. The vent
line at the nacelle contains an inline flame arrester.
l. Engine Oil-to-Fuel Heat Exchanger. An
engine oil-to-fuel heat exchanger, located on each
engine accessory case, operates continuously and
automatically to heat the fuel delivered to the engine
sufficiently to prevent the freezing of any water, which
the fuel might contain. The temperature of the
delivered fuel is thermostatically regulated to remain
between +21 °C and +32 °C.
2-42. FUEL SYSTEM MANAGEMENT.
a. Fuel Transfer System. Fuel in the auxiliary
tanks will be used first. During transfer of auxiliary
fuel, which is automatically controlled, the nacelle
tanks are maintained full. A swing check valve in the
gravity feed line from the outboard wing prevents
reverse fuel flow. Normal gravity transfer of the main
wing fuel into the nacelle tanks will begin when
auxiliary fuel is exhausted. The system will gravity
feed fuel only to its respective side, i.e. left or right.
Refer to Figure 2-20. Fuel will not gravitate through
the crossfeed system.
b. Operation with Failed Engine-Driven Boost
Pump or Standby Pump. Two pumps in each fuel
system provide inlet head pressure to the engine-
driven primary high-pressure fuel pump, and if
crossfeed is used, a third pump, the standby fuel pump
from the opposite system, will supply the required
pressure. Refer to Figure 2-21. Operation under this
condition will result in an unbalanced fuel load as fuel
from one system will be supplied to both engines while
all fuel from the system with the failed engine driven
and standby boost pumps will remain unused. A triple
failure, which is highly unlikely, would result in the
engine driven primary pump operating without inlet
head pressure. Should this situation occur, the
affected engine can continue to operate from its own
fuel supply on its engine-driven primary high-pressure