Chapter 8

Fuel System

Main Menu

SYSTEM DESCRIPTION

 

NOTE: If the engines are running and you are going to change the fuel in the center tank to "0" using the FS drop down menus then you MUST turn the center fuel pumps off before making the change or enter some number above "0" in the center tank. Fore example, enter 5 lbs or 5 gallons for the center tank. Failure to do so might result in both engines flaming out.

 

GENERAL

 

The fuel system consists of three tanks and a crossfeed manifold for fuel management. Electric pumps supply fuel to the engines and APU under positive pressure. The three tanks - left main, center, and right main - are integral parts of the wing structure.

 

FUEL QUANTITY AND INDICATING

 

Probes in each tank provide fuel quantity information to cockpit sensors that show fuel in individual tanks and total fuel on board. To test the fuel indicating system (STEAM & COMBO), click on the test knob on the fuel indicator. Each tank will indicate 3,000 with a total fuel quantity of 9,000. The gross weight display indicates aircraft zero fuel weight (ZFW) plus 9,000 pounds.

 

AIRCRAFT GROSS WEIGHT/ZERO FUEL

 

The fuel quantity indicator also shows aircraft gross weight. The ZFW switch (scroll pushbuttons on GLASS) on the fuel quantity indicator sets aircraft zero fuel weight. The switch is clicked and then can be adjusted by placing the mouse on the left or right side of the knob. After three seconds of inactivity, the gross weight mode will become the active mode. In GLASS, push the appropriate scroll button to set desired ZFW in the readout. When the button is released, fuel quantity is added to the ZFW to produce the aircraft gross weight. As fuel is used, the gross weight display decreases to show the aircraft actual weight.

 

FUEL SHUTOFF VALVES

 

Pulling a fire control handle closes a fuel valve in the supply line of the corresponding engine, cutting off fuel to that engine. Pushing the handle in opens the valve. Shutting down the APU with the master switch, fire control switch, or automatic protection closes the APU fuel shutoff valve.

 

MAIN AND CENTER TANKS

 

Left and right main tanks each have two pumps, one on each AC bus, arranged in parallel. Main tank pimps normally supply fuel directly to their respective engines. The two pumps in the center tank, on of each AC bus, are arranged in series, creating higher pressure than the left and right tank pumps. The higher pressure ensures center tank fuel is used first. Fuel from the center tank pumps flows directly to the left and right engine supply lines through poppet valves. 

 

A 28-volt DC start pump in the right tank supplies fuel for APU or engine starting if AC power is not available. The pump is powered from the DC bus.

 

CROSSFEED MANIFOLD

 

A crossfeed valve in the fuel manifold between the left and right tanks can be opened to supply both engines and the APU from either tank. The valve is mechanically controlled by a lever on the forward pedestal. The lever is normally forward in the OFF position, closing the valve. With the lever in the aft, ON position, the valve is open.

 

APU FUEL SYSTEM

 

OPERATION

 

The APU fuel uses the same fuel feed and the right engine. Normal fuel supply is from the right tank, but with fuel pump and crossfeed selection, any tank can provide APU fuel. A 28-volt DC start pump in the right tank, powered from the DC bus, supplies fuel for APU if AC power is not available. The start pump is located on the overhead panel.

 

APU FUEL VALVE

 

Placing the APU master switch to the RUN or START opens a fuel shutoff valve in the APU fuel supply line. When the APU is shut down, the valve is closed.

 

 

Fuel System

 

CONTROLS AND INDICATORS

 

FUEL QUANTITY DISPLAY - STEAM & COMBO

 

 

LOCATION: Main Panel

 

FUEL QUANTITY INDICATOR

 

Indicates individual tank quantity, total fuel quantity, and aircraft gross weight. Displays 8s when annunciator/digital lights test switch is pressed.

 

TEST SWITCH

 

When switch is clicked, each tank indicates 3000. Total fuel indicates 9000. Gross weight display indicates ZFW plus 9000.

 

ZERO FUEL WEIGHT SWITCH

 

The ZFW switch on the fuel quantity indicator sets aircraft zero fuel weight. The switch can be clicked in the center to view the ZFW. Clicking the left or right side of the knob will also activate the ZFW mode. When active the ZFW can be adjusted by clicking on the left or right side of the switch. After three seconds of inactivity, the gross weight mode will become the active mode. As fuel is used, the gross weight display decreases to show the aircraft actual weight.

 

FUEL QUANTITY DISPLAY - GLASS

 

 

LOCATION: Main Panel

 

ALTERNATE CHANNEL INDICATOR

 

Displays letter "B" when alternate channel B selected, blank when channel A selected.

 

FUEL QUANTITY INDICATOR

 

Indicates individual tank quantity, total fuel quantity, and aircraft gross weight. The Gross weight window can also display zero fuel weight valve. 

Displays 8s when annunciator/digital lights test switch is pressed.

 

ZERO FUEL WEIGHT SCROLL PUSHBUTTONS

 

Momentary push either pushbutton to display zero fuel weight value in GROSS WT window. is displayed in TOTAL FUEL window. Push and hold desired pushbutton to change the value. Up increases ZFW and down decreases ZFW.

 

ALTERNATE CHANNEL SELECT PUSHBUTTON

 

Push to select an alternate channel (Channel A or Channel B) for processing and transmitting fuel quantity data.

 

 

FUEL CROSSFEED

 

 

LOCATION: Throttle Panel

 

FUEL CROSSFEED LEVER

 

    OFF - Fuel crossfeed valve is closed, allowing left fuel tank to supply fuel to the left engine and the right tank to supply fuel to the right engine

               and APU.

 

    ON - Opens the fuel crossfeed valve allowing either left or right tanks to supply fuel to both engines and APU.

 

FUEL TANK PUMP SWITCHES

 

 

LOCATION: Overhead Panel

 

DC START PUMP SWITCHES

 

    ON - DC bus power used to power start pump for APU or engine starting.

 

FUEL TANK PUMP SWITCHES

 

Controls the fuel pumps for the left, center, and right fuel tanks.

 

- Respective fuel pressure is low.

 

FUEL LEVEL LOW - CAWS message appears in GLASS only. Indicates that either main tank fuel quantity is below 2,500 pounds.

 

 

SCHEMATICS