Fuel System

Question 1

How many tanks are in the KJ wings? What other ones?

Answer 1

Four integral wing main tanks
Two auxiliary tanks

Two external tanks between the outboard and inboard nacelles. They are mounted on pylons beneath the wings.

All the fuel tanks, except the fuselage tank, are equipped with an internal reticulated, explosive-suppressant, conductive foam baffle system. The baffles prevent fuel surges at all wing attitudes and permit fuel to flow inboard only by flapper valves.

Question 2

Describe the main tanks

Answer 2

The main tanks are integral to the wing and are formed by front and rear wing beams. Two ends are bulkheads. Each main tank contains two fuel pumps; one boost pump and one transfer pump.

Question 3

Describe the outboard tanks

Answer 3

No 1 and 4 are divided into three sections (outboard, center, and inboard) by baffles. The inboard section contains a boost pump, flapper valves, and a surge box. The center section contains a tank fuel level control valve, an over wing filler port, and a percolator tube, which allows fuel to travel to the outboard section during refueling and aids in fuel flow during wing-high attitudes.

Question 4

Describe the inboard tanks

Answer 4

The inboard tanks no 2 and 3 have a boost pump and transfer pump, flapper valves, and a surge box, but they have only one section with no baffles or percolator tube.

Question 5

What do the main tank surge boxes do?

Answer 5

The main tank surge boxes prevent the fuel boost pumps from becoming fuel starved during nose-down, or negative-gravity attitudes by keeping the boost pumps submerged in fuel.

Question 6

Describe the auxiliary tanks

Answer 6

The aux tanks are three-cell rubber bladder tanks made of four ply rubber construction. Free flow of fuel is among the cells. They are located in the center section of the wing.

Each tank is supported by fasteners and lacing on the top, by plumbing along the sides, and a fiberglass board on the bottom. A sump in the center cell extends down to an access panel in the undersurface of the wing. A transfer pump is mounted on this access panel. The pump outlet line is connected to the cross-ship manifold.

Question 7

Describe the external tanks

Answer 7

They are cylindrical all-metal external tanks. They are mounted on pylons under the wings between the inboard and outboard engines. Tank quantity is 1,309 gallons with foam and 1,379 gallons without foam.

The external tanks consist of three separate sections held together by two large locking clamps. Two internal bulkheads are bolted to the center section to stiffen the tank and prevent fuel from surging fore and aft. A surge box of welded construction is at the bottom of the center section. Two transfer pumps are mounted in the surge box of each tank. Two flapper valves are installed on the surge box to allow fuel to flow in from the center section. Two transfer tubes, each containing flapper valves, allow fuel to flow into the surge box from the front and rear sections.

Question 8

Describe the fuel tank vent system

Answer 8

The fuel tank vent system vents all fuel tanks to the atmosphere to equalize pressure and prevent damage to the wing or tank. The outboard and inboard tanks vent pressure overboard through vents in the bottom of the wing just outboard of the AR pods. The tanks vent from the bottom of the outer wing. The outer most vent is from the outboard tank and the inner most vent is from the inboard tank.

Tanks No 2 and 3 and the left and right auxiliary tanks have a wrap-around vent system. Tanks No 1 and 4 are vented by float-controlled vent valves. The external tanks are vented through the space at the top of the baffles, separating the tank compartments, and through the fuel vent line.

Question 9

Describe the wrap-around vent system

Answer 9

The wrap-around vent system permits venting of the inboard tanks, even if the aircraft is not wings level. Inboard tanks have no vent valves. Tubes are arranged so that one end is always above fuel level regardless of aircraft attitude. The vent tank is evacuated in the same manner as the outboard tank.

In the auxiliary tanks (wrap-around), fuel is removed by an eductor or a jet pump at the bottom of the vent tank

Question 10

What are the float-controlled vent valves

Answer 10

They are on the outboard tanks to prevent fuel loss overboard on the ground when the aircraft is not in a wings level attitude and in flight when the wings deflect upward.

Question 11

Describe the external tank vent system

Answer 11

The external tank vent system line runs from the forward end of the center compartment of the tank through the pylon and up into the wing trailing edge where it vents to the atmosphere. The vent line is at the top of the tank and runs upward to the wing

Question 12

What are the fuel level control valves

Answer 12

The fuel level control valves automatically stop fuel from flowing into the tank when it’s full. They are located in each fuel tank to control fuel flow into their respective tanks. They require electrical power to both solenoids to open and are electronically controlled by the fuel management controller.

The no 1 and no 4 main tanks each have 3 flcvs; 2 flcvs compensate for wing flex and allow a greater fuel load in flight. The third flcv is installed, but not operational. The no 2 and no 3 tanks, auxiliary tanks, and external tanks each contain 1 flcv

The FLCVS are spring-loaded closed if electrical power to both solenoids is interrupted, or closed by the floats if tank capacity is reached. The FLCVs can also be programmed to stop filling the tank at any preset quantity

Question 13

Describe the fuel pumps

Answer 13

There are two fuel pumps in each main fuel tank: a boost pump and a transfer pump. The 15 to 24 psi, three-phase, ac-powered boost pumps ensure fuel flow to the engines. The 28 to 40 psi, three-phase, ac-powered fuel transfer pump provides fuel transfer and jettisoning capabilities.

The left and right aux tanks each have one 28 to 40 psi, three-phase, ac-powered transfer pump that provides fuel transfer and jettisoning capability

Each external tank has two transfer pumps with only one used for normal operations. Each time an external tank transfer switch is switched ON, the pumps alternate to ensure equal operating time

Boost pump and transfer pumps are identical in operation and only differ in physical size and output. An access panel located on the aft wing beam allows boost pump inspection, removal, or replacement

The transfer pumps leave 1520 lbs outboard and inboard

Question 14

Describe the main tank water removal system

Answer 14

The main tank water removal system provides continuous water removal from the low point in the tank during boost pump operation. It also maintains the fuel level around the boost pump in the surge box when the aircraft is in a nose-down attitude with low fuel level in the tank

The fingers sit a quarter inch off the floor of the tank. Suction pressure is developed through boost pump discharge pressure. Condensation and fuel are sucked up and deposited into the surge box for the pump to the transfer to the engine.

Question 15

Fuel quantity indicating system

Answer 15

The fuel quantity indicating system accurately measures fuel levels inside the fuel tanks using probes and compensators. The probes are wired in series to the compensator. The compensators measure density of the fuel, not the quantity, providing a more accurate fuel level reading

Outboard tanks: 5 probes, 1 compensator
Inboard tanks: 4 probes, 1 compensator
Aux tanks: 3 probes, 1 compensator
Ext tanks: 4 probes, 1 compensator

Question 16

Fuel management controller does what?

Answer 16

The dual fuel management controller (FMC) monitors and controls the basic aircraft fuel system. The FMC is located on the cargo compartment aft overhead equipment rack. The FMC performs a power-up, built-in-test BIT, and continuous BIT during normal operation.

Question 17

What is the purpose of the KJ fuel system?

Answer 17

Supply fuel to the four engines and the APU

Question 18

How many fuel pumps are in each main tank?

Answer 18

Each main tank contains two fuel pumps: one boost and one transfer pump

Question 19

What is the function of the water removal system?

Answer 19

Provides continuous water removal from the low point in the tank during boost pump operation

Question 20

The boost pump and transfer pump have an internal thermal switch that shuts the pump down when internal (bearing) temperature reaches ___ degrees?

Answer 20

375 degrees

Question 21

What happens to fuel valves in the event of a power failure?

Answer 21

In case of power failure, the fuel valves hold the last energized position.

Question 22

What does the cross-ship valve do?

Answer 22

The cross-ship valve is used for refueling, defueling, transferring fuel from one wing to the other, and transferring fuel to or from the fuselage tank.

Question 23

What are the dump valves?

Answer 23

Dump valve switches control the dump mast shutoff valves and the interconnect valves. When the guards are lowered, the switches move to the closed position, closing the interconnect valve and stopping the fuel dumping process. In flight, when the switches are placed in the open position, the dump shutoff valves and interconnect valves open to allow fuel to dump overboard. If the AR pumps are being used for dumping, the interconnect valves will remain closed or close upon activation to prevent high pressure fuel from entering the cross-ship manifold.

Question 24

How long does it take to complete SPR draining? How many cycles to completely drain SPR manifold?

Answer 24

2.5 minutes per cycle

2 cycles to completely drain the manifold

Question 25

How do you check the aux tank level?

Answer 25

The aux tank magnetic sight provides for visual indication of the tank level. The magnetic sight gauge is located on the underside of the wing center-section for each aux fuel tank. The gauge consists of three components: a mounting base and outer tube, a float, and a calibrated gauge stick.

The stick is marked in 200-pound increments and is calibrated for fuel at 6.7 pounds per gallon

Question 26

What are the fuel weight limits for each tank?

Answer 26

Tank 1 & 4: 8310 lbs
Tank 2 & 3: 7,650 lbs
Ext: 8,900 lbs
Aux: 5,810 lbs
Fuselage: 24,390 lbs

Question 27

What is the function of the fuel tank foam?

Answer 27

Explosion-suppressant

Question 28

How many FLCVs are in each outboard tank?

Answer 28

Three

Question 29

In what position will the fuel valves be if a power failure is experienced?

Answer 29

The fuel valves will hold the last energized position

Question 30

What are the steps when you have a fuel spill without fire during ground refueling?

Answer 30

1. Cease fueling operation.
2. Shut down power unit and refueling unit, if required.
3. Position personnel for fire protection.
4. Notify fire department.

Question 31

What should you do when you have a fuel spill with a fire during ground refueling?

Answer 31

1. Cease fueling operation.
2. Notify fire department
3. Shut down power unit and refueling unit, if required
4. Attempt to extinguish fire
5. Move aircraft and servicing unit, if possible.
6. Move surrounding aircraft, if necessary

Question 32

What fuels can the KJ use?

Answer 32

JP-8
JP-5
JP-4
A-1
TS-1

Question 33

What do the engine start switches do?

Answer 33

The START and RUN positions control the boost pumps for their respective main tanks

Question 34

What happens when a fire handle is pulled?

Answer 34

The firewall fuel shutoff valve is closed, and the shutoff valve in the engine fuel pump and metering unit is closed.

APU: the APU fuel supply shutoff valve is closed

Question 35

How is the APU fueled?

Answer 35

Fuel is gravity fed from the no 2 main fuel tank through a motor operated shutoff valve located in the no 2 dry bay.

Question 36

How does the engine fuel system work?

Answer 36

The engine fuel system delivers filtered metered fuel for combustion, provides pressurized fuel to operate the CVG system, and provides supplemental cooling for engine return oil.

Question 37

What are the major components of the engine fuel system?

Answer 37

The FPMU, CVG hydraulic actuator, the FCOC, fuel flow sensor, and fuel nozzles

Question 38

Describe the flow of fuel to the engine

Answer 38

Fuel entering the FPMU is routed through a centrifugal pump which provides vapor free fuel at a pressure sufficient for high pressure (gear-type) pump use. From the centrifugal pump outlet, fuel flows through the FCOC to cool engine return oil and heat the fuel to minimize engine fuel system icing. Fuel leaving the FCOC is directed through a bypassable fuel filter and the high pressure fuel pump before entering the fuel metering portion of the FPMU. A pressure relief valve, located in the high pressure pump outlet line, opens if pressure is excessive. The relief valve pressure setting is higher than the gear pump will deliver in normal operation. A solenoid-controlled air vent valve enables any air in the system to bled off during starting. The air vent valve closes when substantially air-free fuel flow is attained. On engine shutdown, the air vent valve remains closed to ensure air-free fuel is maintained between the gear pump and FPMU. Dual FADECs (one controlling and the other backup) control the flow of metered fuel to the pressure raising valve. The pressure raising valve ensures that adequate system pressure is maintained. Normally the pressure raising valve is open. When the FADEC commands the fuel latching shutoff valve closed, it causes the pressure raising valve to close and route fuel back to the high pressure pump inlet. This stops fuel flow to the fuel nozzles and prevents fuel draining from the combustion chambers on engine shutdown. A fuel flow sensor monitors fuel flow. The sensor is located in the line between the FPMU and the fuel manifold. From the fuel manifold, metered fuel flows to the fuel nozzles. The fuel nozzles provide a pressurized fine spray of fuel to the combustors.