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the FUEL IMBALANCE amber CAS.
The fuel quantity signal conditioner software determines low fuel conditions
from the filtered fuel quantity. The L or R FUEL QTY LOW amber
CAS is generated when fuel quantity is less than 350 pounds.
The following CAS illuminations are specific to the fuel quantity indicating
system:
CAS Color Description
FUEL IMBALANCE Amber A fuel imbalance exists between the left and
right wing tanks.
FUEL QTY LOW Amber The fuel quantity in the associated (L or R)
wing tank is approaching a minimum desired
level for flight.
FUEL QTY FAULT White - When message preceded by L or R:
A fault is detected in the associated channel
of the fuel quantity indicating system.
- When message not preceded by L or R:
The fuselage fuel probe is invalid or attitude
input from the AHRS to the fuel quantity
indicating system is invalid.
Pilot’s Manual
2-36 PM-126A
FUEL INDICATING SYSTEM SCHEMATIC
Figure 2-7
FUEL QUANTITY
SIGNAL CONDITIONER
LEFT
WING
TANK
MAINTENANCE
INTERFACE
ADAPTER
FLIGHT
MANAGEMENT
SYSTEM
DAU
#1
DAU
#2
EICAS
RIGHT
WING
TANK
28 VDC
R QTY
28 VDC
L QTY
FUEL
PROBE
SIGNAL
FUEL
PROBE
SIGNAL
FUEL
PROBE
SIGNAL
FUSELAGE
TANK
A28-0001
SPPR
REFUELING
CONTROL PANEL
/
l b s
LEFT
WOW
RELAY
PANEL
FUEL IMBALANCE (amber)
L R FUEL QTY LOW (amber)
L R FUEL QTY FAULT (white)
Pilot’s Manual
PM-126A 2-37
RAM AIR FUEL VENT SYSTEM
The fuel vent system provides ram air pressure to all interconnected
components of the fuel system to ensure positive pressure during all
flight conditions. A flush-mounted ram air scoop (NACA vent scoop)
located on the left side of the fuselage (forward of the engine) admits
pressure to the fuselage tank main vent system. The main vent system
pressurizes the wing tanks through the fuel vent/expansion lines. The
fuselage fuel vent/expansion lines are each connected to a separate
sump that has a moisture drain valve. Overpressurization due to thermal
expansion in the wing tanks is relieved through the left and right
expansion lines to the fuselage tank. Overpressurization of the fuselage
tank is relieved overboard through the NACA vent scoop. The vacuum/
pressure relief valve is a backup for the NACA vent scoop.
SINGLE-POINT PRESSURE REFUELING (SPPR) SYSTEM
The Single-Point Pressure Refueling (SPPR) system allows the entire
fuel system to be serviced through a SPPR adapter located on the right
side of the aircraft below the engine pylon. The SPPR incorporates a
precheck system which allows the operator to check the operation of
the system shutoff valves before commencing refuel operations. The
major system components are the refueling adapter, refueling panel,
refuel shutoff valve, pilot valve, precheck valve, and associated plumbing
and wiring.
Electrical power to operate the system indicator lights, solenoid valves
and fuel quantity signal conditioner is 28-vdc supplied from the EMER
BATT hot bus through the PWR ON switch on the refuel control panel.
The refuel shutoff valve is controlled by the pilot valve located at the
high point in the fuselage tank. When refueling pressure is applied to
the system through the pressure refueling adapter, pressurized fuel is
applied to the refuel shutoff valve. This pressure is applied to both
sides of the valve poppet. If the pilot valve is open, some of the pressure
acting to hold the valve closed will be vented through the pilot valve
and the pressure acting to unseat the poppet will drive the valve open
against the spring tension. When the tank fills, the pilot valve will close,
fuel pressure on both sides of the refuel shutoff valve poppet will
equalize, and spring tension will drive the valve closed. If the refuel
shutoff valve malfunctions, fuel will vent out of the NACA vent scoop
to prevent overpressurization of the fuselage tank.
Pilot’s Manual
2-38 PM-126A
PRECHECK VALVE
The precheck valve is used to check operation of the system shutoff
valve before full refueling procedures are commenced. When the precheck
valve is set to PRECHECK OPEN and refuel pressure is applied
to the refuel adapter, fuel will be admitted to the precheck line. The
shutoff valve will open and fuel will flow into the fuselage tank. The
fuel in the precheck line will empty into a float basin at the pilot valve.
When the basin fills, the pilot valve float will close the pilot valve,
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