TM 55-1510-219-10
pump on the side from which crossfeed is desired. During
crossfeed operation with firewall fuel valve closed,
auxiliary tank fuel will not crossfeed. When the crossfeed
mode is energized, a green FUEL CROSSFEED light on
the caution/advisory panel will illuminate. Crossfeed
system operation is described in Chapter 9. The
crossfeed valve is protected by a 5-ampere circuit breaker
placarded CROSSFEED VALVE located on the overhead
circuit breaker panel (fig. 2-26).
f.
Firewall Shutoff Valves.
CAUTION
Do not use the fuel firewall shutoff
valve to shut down an engine,
except in an emergency. The
engine-driven highpressure fuel
pump obtains essential lubrication
from fuel flow. When an engine is
operating,
this
pump
may
be
severely damaged (while cavitating)
if the firewall valve is closed before
the condition lever is moved to the
FUEL CUTOFF position.
The fuel system incorporates a fuel line shutoff
valve mounted on each engine firewall. The firewall
shutoff
valves
close
automatically
when
the
fire
extinguisher T-handles on the instrument panel are pulled
out. The firewall shutoff valves receive electrical power
from the main buses and also from the hot battery bus
which is connected directly to the battery. The valves are
protected by circuit breakers placarded FIREWALL
VALVE #1 or #2 on the overhead circuit breaker panel
(fig. 2-26), and FIREWALL SHUTOFF #1 or #2 on the
hot battery bus circuit breaker board.
g.
Fuel Sump Drains. A sump drain wrench is
provided in the aircraft loose tools to simplify draining a
small amount of fuel from the sump drain. There are five
sump drains and one filter drain in each wing (Table 2-3).
An additional drain for the extended range fuel system
line extends through the bottom of the wing center section
adjacent to the fuselage. Anytime the extended range
system is in use, a part of the preflight inspection would
consist of draining a small amount of fuel from this drain
to check for fuel contamination. Whenever the extended
range system is removed from the aircraft and the fuel
line is capped off in the fuselage, the remaining fuel in the
line shall be drained.
h.
Fuel Drain Collector System. 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. 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 arrestor and then
downward to a drain manifold on the underside of the
nacelle.
i.
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 arrestor.
j.
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 it might contain.
The temperature of the delivered fuel is thermostatically
regulated
to
remain
between
21°C
and
32°C.
2-34
Table 2-3. Fuel Sump Drain Locations
