FUEL
Description
Aircraft Operations Manual
9/1.1
PAGE
2
2.
MAIN COMPONENTS AND SUBSYSTEMS
2.1
Fuel storage
Each fuel tank consists of two cells, integral with
the wing, one inboard and one outboard of the en-
gine nacelle. Baffling is provided inside the fuel cells
to prevent rapid displacements of fuel within the cell
during aircraft maneuvering. The two cells are inter-
connected by a fuel hose and a vent line. A flapper
valve in the fuel line permits fuel flow from the out-
board to the inboard cell only. Each outboard cell
has a filler neck for gravity fueling.
The lower end of the inboard cell has a hopper tank
with a capacity of 200 lb (90 kg). Four flapper
valves permit fuel to flow into, but not out of the
hopper tank to provide fuel for the engine feed sys-
tem at all times. A negative ”G” suction feed inlet
canister is attached to the wing structure within the
hopper tank and surrounds the suction feed inlet
check valve. The canister insures continuous fuel
feed during limited uncoordinated or negative ”G”
aircraft maneuvering. A drain valve is incorporated
in the lowest part of the hopper tank.
The inboard cell is vented to the outboard cell. The
outboard cell is then vented overboard through a
vent line at the underside of the wing. The vent sys-
tem maintains a slight overpressure in the tanks
during flight. A baffle in the outboard cell prevents
fuel from sloshing out through the vent. The vent
will also provide for overflow in case of overfilling
when fueling, e.g. due to a failure in the shutoff sys-
tem.
2.2
Fuel distribution
Pressure fueling system
A single point receptacle and refuel/defuel control
panel is located in the right wing leading edge, out-
board of the engine nacelle. The control panel is
supplied direct from the batteries and does not re-
quire any power to be on in the cockpit. A refueling/
defueling line connects the receptacle with a refuel-
ing shutoff valve in each tank and with a defueling
valve on the crossfeed line.
The refueling shutoff valves are solenoid controlled
and actuated by the fueling pressure. They are lo-
cated inside the inboard tank cells. The outboard
cells are replenished by overflow through the vent
line from the inboard cells.
Optical sensors are used to determine mid
−
level
and full level. When activated, the selected sensor
interrupts electrical power to the affected refueling
shutoff valve solenoid and the valve closes.
If the full level detection fails, an overfill float switch
in each cell will interrupt the power and turn on the
corresponding OVERFULL light on the refuel/defuel
panel.
The defueling valve is operated by a DC electric
motor and is of the same type as the interconnect,
crossfeed and fire shutoff valves
Engine feed system
A fuel feed line connects each tank with the engine
on the same side. A crossfeed line with a shutoff
valve interconnects the two feed lines. A suction
inlet and a standby pump with inlet for the feed line
are located in each hopper tank. Check valves in
the inlets prevent return flow into the tank.
An engine
−
driven main pump on each engine draws
fuel from the tank. A main pump differential pres-
sure switch, sensing the differential pressure across
the pump, actuates the corresponding standby
pump if the main pump fails, provided that the L/R
STBY pump switch is set in the guarded AUTO
position. The main pump differential pressure switch
also actuates the MAIN PUMP warning light on the
overhead fuel panel. In case of engine shutdown, a
condition lever actuated switch will inhibit the stand-
by pump auto starting.
Another pressure switch senses the pressure in the
feed line upstream of the main pump and activates
the STBY PRESS light on the fuel panel to indicate
standby pump operation. In case of standby pump
failure, the standby pump on the opposite side can
be switched on to supply fuel through the cross-
feed. The capacity of each standby pump is suffi-
cient to supply both engines at all power settings.
A fuel heater and a fuel filter are incorporated in the
engine installation. See AOM 17.1 for description.
An electrical shutoff valve at each engine nacelle
will shut off the fuel supply to the engine if the fire
handle is pulled. The L/R VALVE CLOSED light on
Jun 01/20
