Why do the engines normally consume center-tank fuel before main-tank fuel when the applicable boost pumps are operating?, The center-tank boost pumps operate continuously, while the main-tank pumps are automatically switched off whenever center-tank fuel is available., The center-tank boost pumps supply fuel to the engine-feed manifold at a higher pressure than the main-tank boost pumps., The crossfeed valve automatically connects the center tank directly to both engines whenever center-tank quantity is above the minimum limit., A surge-tank pressure-relief valve is found latched open during a maintenance inspection. What should this condition indicate to the engineer?, The surge tank has reached its normal fuel-overflow limit and the pressure-relief valve must remain open until the tank quantity decreases., The fuel vent system has experienced an excessive positive or negative pressure differential and the open valve is evidence of a vent-system problem., The Nitrogen Generation System has intentionally opened the valve to reduce center-tank oxygen concentration., During pressure refueling, the blue refueling-valve OPEN light is illuminated but no fuel is entering the selected tank. Why can this indication exist without actual valve opening?, The light indicates only that the tank float switch is in the NOT FULL condition., The light illuminates whenever the refueling-panel door is open, regardless of refueling-valve control-switch position., The light indicates electrical power to the refueling-valve solenoid, but fuel pressure must also be available before the valve can physically open., During suction defueling, why can main tank 1 not be suction-defueled independently of main tank 2?, Main tank 1 suction defueling must occur at the same time as main tank 2 because air entering the common manifold when either tank empties stops fuel flow., Main tank 1 has no direct connection to the defueling manifold and must be emptied through main tank 2., The crossfeed valve is electrically prevented from opening unless both main-tank boost pumps are operating., The left center-tank boost-pump switch is ON and pump pressure remains at or below 18 pounds per square inch gauge. What protective action occurs if this condition persists?, After approximately 15 seconds, the automatic shutoff circuit de-energizes the pump-control relays and removes electrical power from the pump., The Ground Fault Interrupter immediately trips and can only be reset after the aircraft electrical system is depowered., The corresponding main-tank boost pump automatically increases its discharge pressure to maintain center-tank fuel feed., Both center-tank boost pumps become unavailable while usable fuel remains in the center tank. Why can the engines not suction-feed directly from the center tank?, The center tank does not have bypass valves, so fuel cannot reach the engine-feed manifolds from the center tank without operating boost pumps., The center-tank feed lines are isolated automatically whenever boost-pump pressure falls below 18 pounds per square inch gauge., The engine fuel spar valves close whenever both center-tank boost pumps lose pressure., The aircraft hot battery bus voltage falls below 22 volts direct current during a condition requiring an engine fuel spar valve to close. How is valve-closing capability maintained?, The emergency fuel shutoff battery automatically supplies the valve-actuator circuits when the hot battery bus falls below the specified voltage., Direct Current Bus 2 automatically connects directly to the fuel spar valve actuator through the crossfeed-valve circuit., The engine Electronic Engine Control commands the main battery contactor closed regardless of battery-switch position., The Auxiliary Power Unit is operating with the crossfeed valve closed. Main tank 1 boost-pump pressure and the left center-tank boost-pump pressure are both low, with no protective shutdown fault present. What fuel-system response is expected?, The crossfeed valve automatically opens so that main tank 2 can supply the Auxiliary Power Unit., The Auxiliary Power Unit Direct Current boost pump automatically operates to supply fuel to the Auxiliary Power Unit., The Auxiliary Power Unit fuel shutoff valve closes because two normal boost-pump sources have been lost., How does the Fuel Quantity Indicating System compensate for different fuel types or changes in fuel dielectric properties when calculating fuel quantity?, A compensator in each tank provides a signal proportional to fuel dielectric, allowing the Fuel Quantity Processor Unit to correct the tank-unit measurements., Each tank unit independently measures fuel density and sends a corrected fuel-weight value directly to the display system., The Fuel Management Computer compares measured fuel volume with fuel temperature and calculates dielectric correction externally., Fuel quantity is being manually determined using the measuring sticks because the normal Fuel Quantity Indicating System is unavailable. Why is measuring-stick height alone insufficient to determine the actual quantity of fuel?, Fuel temperature and boost-pump pressure must be applied to each measuring-stick reading before fuel quantity can be calculated., The measured fuel height must be corrected using compensator capacitance obtained from the Fuel Quantity Processor Unit., Aircraft pitch and roll must also be determined and used with the measured fuel height in the applicable conversion tables.

ATA 28

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