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B777 CATHAY STUDY GUIDE > FUEL SYSTEM > Flashcards

FUEL SYSTEM Flashcards

1
Q

How many fuel tanks are there?

A

3+2
Left, Centre, Right and two surge tanks

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2
Q

How many fuel pumps are there in the system?

A

7
2 AC driven pumps in the Left tank
2 AC driven pumps in the Right tank
2 AC driven override/jettison pumps in the Centre tank
1 DC driven pump in the Left tank

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3
Q

When is the DC pump operational?

A

When the AC pump is not powered
It provides fuel to the APU until AC power is established

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4
Q

How are the Centre tank pumps different from the Left/Right tanks fuel pumps?

A

It’s output pressure is higher (36 psi) so the overrides the Left and Right fuel pumps as a supplier of fuel to the engines when fuel is available in the Centre tank

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5
Q

How many Jettison pumps are there and where are they located?

A

There are 4 jettison pumps
2 in the Centre tank, combined with the normal AC pumps
1 in each outer wing tank

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6
Q

What inputs are used by the FQIS (Fuel Quantity Indicating System) to calculate fuel quantity?

A

Fuel height and density

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7
Q

Where are the fuel temperature and minimum fuel temperature displayed?

A

Fuel temperature is shown on the EICAS display and the fuel synoptic.
Minumium fuel temperature is displayed on the fuel synoptic

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8
Q

Where does the minimum fuel temperature information originate from?

A

Temperature entered in the FMS

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9
Q

On the ground with only one power source, how many Centre tank pumps will run?

A

Only one

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10
Q

On the ground, when will both Centre tanks run?

A

When there are two power sources available

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11
Q

What happens when the Centre tank is almost empty?

A

The outer wing tank pumps automatically take over and a scavange pump in the Centre tank transfer any remaining fuel over to the wing tanks

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12
Q

What happens if both main tank pumps output pressure is low?

A

The Engines can draw fuel from it’s corresponding main tank through a suction feed line that bypasses the pumps

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13
Q

When is FUEL IMBALANCE displayed?

A

When the main tanks differ more than 500 kg

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14
Q

What is the total fuel capacity for the B777-300ER?

A

145’500 kg

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15
Q

How can intial “Jettison fuel to remain” value be modified?

A

By the “FUEL TO REMAIN” selector

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16
Q

What is the initial jettison to remain value?

A

Maximum landing weight fuel quantity

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17
Q

If the Center pumps are in the OFF position can they be used for jettison?

A

No, they have to be on to work

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18
Q

When does jettison terminate?

A

When the target value has been reached
Can also be terminated maually

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19
Q

How is the aircraft protected from jettison all fuel overboard?

A

By a standpipe in the fuel tanks that ensure that 5’200 kg remains in the main tanks

20
Q

Fuel density limits?

A

0,7309 - 0,8507

21
Q

What fuels are prohibited to use?

A

JP-4 and Jet B

22
Q

What is the max fuel temperature?

A

49 deg C

23
Q

Min fuel temp for T/O?

A

-40 deg C or 3 deg C above the fuel freezing Point, whichever is higher

24
Q

Fuel capacity in each of the 3 fuel tanks on the -300ER?

A

Mains - 31’300 kg each
Center tank - 82’900 kg

25
Q

Max fuel imbalance between main tanks for Taxi, T/O and landing?

A

1’360 kg (3000 lbs) if tot main tanks exceeds 55’791 kg
2’041 kg (4500 lbs) if tot main tanks is less than 40’823 kg

26
Q

How much fuel in kg/min can be jettisoned from the B777-300ER?

A

With fuel in centre tank: 2’500 kg/min
With centre tank empty: 1’400 kg/min

27
Q

When will the EICAS “FUEL QTY LOW” show?

A

When either main tank is below 2’041 kg of fuel and it will disappear at 2’200 kg

28
Q

What is the output pressure in PSI of the main tank AC fuel pumps?

A

12 PSI

29
Q

What is the output pressure in PSI of the left main tank DC fuel pump?

A

24 PSI

30
Q

What is the output pressure in PSI of the center tank AC fuel pumps?

A

36 PSI

31
Q

Why is the center tank fuel used before the main tanks fuel?

A

Reasons to use the Center Tank fuel first are to reduce stress on the fuselage and also to get rid of fuel below the cabin in case of a fuel related fire

32
Q

How would you know that the fuel to the engines are provided by suction and not by pump action?

A

The fuel flow line on the fuel synoptic turns amber when fuel is provided by suction.

33
Q

Describe how the totalizer fuel quantity is measured on the B777?

A

The FQIS(Fuel Quantity Indicating System) in the 777 works by bouncing sound waves around the fuel tank
Based on the reception data returned by the probes (VOS is Speed of Sound in the maintenance page) – the FQIS calculates the volume of fuel in the tank by measuring fuel height. Built in Densiometers provide the fuel specific gravity (SG) to turn the volume into mass by multiplying volume and density to calculate fuel weight.

34
Q

How many fuel sensors are there in the main- and the center tanks?

A

28 in each main
20 in the center

35
Q

What is the certification error tolerance for the fuel totalizer indicating system?

A

1%, which means that it’s +- 1’450 kg

36
Q

What is the error rate for the calculated fuel flow system?

A

This error rate is based on Fuel Flow (0.5% of 8000 Kg/Hour) which therefore produces a potential error of 40 Kg/hour, less than the possible error of the Totalizer value and therefore makes it more reliable in the beginning of the flight.

37
Q

Can all fuel from the center and main fuel tanks be jettisoned?

A

All fuel from the center tank can be jettisoned but for the mains there is a standpipe that limits it to 5’200 kg to be remaining in each main tank.

38
Q

How is fuel jettison from the different fuel tanks affected if a fwd CG position is detected?

A

When the aircraft is loaded near its FWD CG, fuel is jettisoned from the Center Tank first to keep the CG within limits. If ELMS senses that the FWD CG limit will be reached, the main tank jettison pumps stops for 7,5 min.

39
Q

How long time after the center tank pumps have been switched off will the scavenge system start to operate?

A

45 min

40
Q

What is the difference between the modified and the old fuel scavenge system?

A

The modified scavenge system means that the jettison pumps in the main tanks provides the motive flow for the Fuel Scavenge jet pumps. In the non-modified systems, the main tank boost pumps provides motive flow for the fuel scavenge pumps. The fuel scavenge pumps will run as long as the boost pumps are running. To stop fuel going into a full main tank, an outlet float operated shutoff valve closes to stop fuel flowing through the discharge line.

41
Q

What is the purpose of the water scavenge jet pumps?
How many are there and how do they operate?

A

There are 4 water scavenge jet pumps in the system. 1 in each main tank and 2 in the center tank. They use motive flow from the main tank boost pumps to operate. Suction through the jet pumps takes fluid from the low points in the tank and sends it to the pump inlets. This prevents water from collecting in the bottom of the tanks.

42
Q

What is an NACA scoop and that is it’s function?

A

NACA scoops (National Advisory Committee for Aeronautics) located near each wing tip, provides the small positive head of pressure on the fuel. This prevents vacuum forming as the fuel is used and also assists the fuel pumps and reduces evaporation. If the tanks are overfilled, this is where the extra fuel will come out. A flame arrestor within the pipe of the vent scoops help prevent any open flame from getting into the tanks.

43
Q

What is the NGS system?

A

Nitrogen Generation System
It separates oxygen from the nitrogen and vents the oxygen overboard. Nitrogen replaces the air in the tank as fuel in the center tank decreases. This keeps the oxygen level well below 12% which makes combination unsustainable.
Its only used in the center tank as that only where the temp can exceed 38 deg C (flashpoint), due to heat increase from the aircon packs

44
Q

What is the flashpoint for jet fuel?

A

38 deg C

45
Q

After how many seconds of low fuel pressure will the center tanks pumps turn off?

A

15 seconds of low pressure

B777 CATHAY STUDY GUIDE (24 decks)

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