I A P 2 0 2 3 . 0 0 1 - A F M / I R I S T E X A N I I P A G E | 39
FOR SIMULATION USE ONLY – NOT A TRAINING AID
The outer probe provides fuel readings until approximately 445±50 pounds, and the
middle probe until approximately 308±50 pounds. The inner probe provides fuel
readings until approximately 20 pounds since the collector tank only has one probe
and divides its capacity equally between the left and right fuel tank readings.
If a fuel probe fails, the amber FUEL BAL caution illuminates and FP FAIL caution
illuminates on the EICAS. If the fuel gage does not show an imbalance, then the
failed probe is not being used to sense fuel.
When the failed probe is being used, the indicated fuel level in that tank drops to the
next fuel probe. For example, if the middle fuel probe fails, the fuel in that tank
appears normal until the fuel drops below 445±50 pounds; it then indicates 308±50
pounds until the fuel burns down below 308±50 pounds. After this point, the fuel
reading appears normal.
Operations
Fuel gravity drains from outboard to inboard wing cavities where transfer jet
pumps supply fuel to and maintain a low, positive pressure in the collector tank. A
fuel pickup valve in the collector tank supplies fuel to the engine.
During inverted flight, a weighted rod in the pickup valve closes off the normal fuel
pickup, and opens the inverted flight fuel pickup. This provides a minimum of 15
seconds of fuel regardless of orientation, and prevents air ingestion into the fuel
system.
A primary jet pump or electric boost pump in the collector tank feeds fuel to the
engine-driven low pressure fuel pump. The low pressure fuel pump supplies fuel to
the engine-driven high pressure fuel pump which supplies fuel to the FMU. The
electric boost pump provides fuel for engine start and serves as a backup to the
engine-driven low pressure fuel pump.
If both the electric boost pump and the engine-driven low pressure pump fail, the
engine-driven high pressure fuel pump will suction feed sufficient fuel for
continued engine operation but will not allow an engine restart. If the engine-driven
high pressure fuel pump fails, the engine will flame out and cannot be restarted.
The fuel supply line to the engine incorporates two manually operated shutoff
valves and a fuel filter. One shutoff valve is provided to isolate the fuel system for
engine or fuel filter maintenance. The firewall shutoff handle in the front cockpit
activates the other shutoff valve, which stops fuel flow to the engine.
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