Fuel System

Question 1

On aircraft with an electric scavenge pump, when is the pump commanded to operate? Where does the scavenged fuel go? How long will it operate?
(AOM Vol II, Ch 12)

Answer 1

• Scavenge commences at reserve tank 2 and 3 transfer initiation.
• Fuel is discharged into number 2 main tank.
• The pump operates for 120 minutes or until low pressure is sensed.

Question 2

When will the fuel system automatically balance itself?

AOM Vol II, Ch 12

Answer 2

• Automatic balancing of the fuel system is accomplished during fuel jettison by the fuel jettison control system.

Question 3

What is the difference between total fuel and calculated fuel? When are the values different?
(AOM Vol II, Ch 11) (AOM VOL II, Ch 12)

Answer 3

• Total fuel is the fuel sensed in the tanks.
• Calculated fuel separates from total fuel when the first engine is started. It uses engine fuel flow subtracted from the fuel sensed at engine start.

Question 4

On taxi out, the EICAS advisory message “FUEL IMBAL 1-4” is displayed. What does this mean? Can you depart? You configure the crossfeed manifold and fuel pumps to bring the fuel imbalance to 2,800 pounds. Is the message still displayed? Can you depart?
(AOM Vol II, Ch 12) (QRH, Ch 12)

Answer 4

• The EICAS advisory indicates a fuel difference between main tanks 1 and 4 of 3,000 pounds or more.
• No.
• The message will still be displayed, because it will not disappear until the difference is less than 1,000 pounds.
• Yes, the limitation is 3,000 pounds.

Question 5

You are overweight for landing and must land. Fuel jettison is required. Per the QRH procedure, you arm jettison system by selecting jettison controller A. How do you know the system is armed for fuel jettison? After entering your desired fuel remaining, ATC asks you how long you will be jettisoning fuel. How can you provide the information?
(AOM Vol II, Ch 12)

Answer 5

• Arming of the fuel jettison system is indicated by an outline of the jettison manifold being displayed on the secondary EICAS Fuel Synoptic Page.
• The jettison time will be displayed on the upper right corner of the Fuel Synoptic Page 90 seconds after jettison is commenced.

Question 6

You are jettisoning fuel using jettison controller A. And, jettison controller A fails. What happens?
(AOM Vol II, Ch 12) (QRH, Ch 12)

Answer 6

• Jettison will terminate and the EICAS message ”>FUEL JETT A” will display.
• Jettison controller B must be selected manually.

Question 7

What is the purpose of the 1 and 4 transfer valves?

AOM Vol II, Ch 12

Answer 7

• They are used during fuel jettison, and;
• They are used in a non-normal procedure if both boost pumps fail in either the number 1 or 4 main tank.

Question 8

You are fully configured for takeoff. What are the positions of the number 2 and 3 crossfeed valves? What are the cockpit indications?
(AOM Vol II, Ch 12)

Answer 8

• The crossfeed valves are closed.

* The flow bars in the crossfeed switches are visible.

Question 9

What does the careted EICAS message “>FUEL OVD CTR L” mean?
(AOM Vol II, Ch 12)

Answer 9

• On the ground, more than 17,000 pounds of fuel is in the center wing tank and the left override/jettison pump is off, or;
• In cruise, more than 4,000 pounds of fuel is in the center wing tank and the left override/jettison pump is off.

Question 10

You are starting the APU. External power is not available. How and from where is fuel supplied to the APU?
(AOM Vol II, Ch 12)

Answer 10

• A DC operated fuel pump is powered by the Main Battery Bus and supplies fuel from the number 2 main tank.