Wing Fuel Pressure Switch
A wing fuel pressure switch is installed to
prevent internal overpressurization of the
wings during transfer of fuselage tank fuel. The
switch, located in the right main wheel well,
deenergizes the fuselage transfer pump when
wing fuel pressure activates the switch.
FUSELAGE FUEL FILL-
TRANSFER OPERATIONS
Fill Operation
Fuel may be pumped from the wings to the
fuselage tank using the FILL position on
the XFER–FILL switch. The FILL position
may be used for CG considerations in flight;
however, it is normally used only during fuel
servicing.
When the XFER–FILL switch is placed to the
FILL position:
• The transfer valve opens.
• The crossflow valve opens.
• The wing standby pumps are energized.
• The fuselage tank float switch is enabled.
NOTE
On 25C airplanes, automatic open-
ing of the fuselage valve also occurs
as a result of selecting the FILL po-
sition on the XFER–FILL switch.
The filling time is shortened as both
lines are open.
Transfer Operations
Transferring fuselage fuel in flight is accom-
plished by using the XFER position on the
XFER–FILL switch. When the switch is placed
in the XFER position:
• The wing standby pumps are disabled.
• The transfer valve opens.
• The crossflow valve opens.
• The fuselage transfer pump is energized.
• T h e w h i t e E M P T Y l i g h t ( p r e s s u r e
switch) is enabled.
NOTE
As fuselage quantity approaches
zero, the crew should be alert for
steady illumination of the white
EMPTY light. Failure to position
the XFER–FILL switch to OFF at
that time can cause damage to the
transfer pump.
When the XFER–FILL switch is placed in the
OFF position:
• The transfer pump is deenergized.
• The transfer valve closes.
• The crossflow valve closes.
• Operation of the wing standby pumps is
once again possible.
An optional method of transferring fuselage
fuel in flight is only possible on airplanes
equipped with the gravity-flow line by using
the OPEN position on the FUS VALVE switch.
However, prior to doing so, it is essential to
first assure that the XFER–FILL switch is off,
and that both wing standby pump switches
are off. Then, when the FUS VALVE switch is
placed in the OPEN position:
• The fuselage valve opens.
• The crossflow valve opens.
When the amount of fuel in the wing tanks be-
gins to decrease, the FUS VALVE switch may
be turned off, and the transfer process may be
completed using the normal transfer procedure.
NOTE
The approved AFM lists several re-
s t r i c t i o n s c o n c e r n i n g w h e n t h e
transfer of fuel from the fuselage
tank may be initiated. See “Fuel
Management,” Section II, of the ap-
proved AFM.
5-13
FOR TRAINING PURPOSES ONLY
LEARJET 20 SERIES PILOT TRAINING MANUAL
FlightSafety
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