AC Fuel Systems

Question 1

Integral Fuel Tank

Answer 1

Part of the wings
Baffles used to prevent fuel moving outwards
“Wet wing design”
+ saves weight

Question 2

Flexible

Answer 2

Rubberised fabric casing attached to AC via chord/buttons
- less capacity than integral
- can puncture easily

Question 3

Drum Fuel System

Answer 3

Rigid design made from metals
Found on large ac

Question 4

Purpose of fuel system

Answer 4

Store fuel/deliver/ensure no contamination/not excessively cold

Question 5

Fuel Booster Pumps are

Answer 5

Low pressure pumps
High flow rate
Three phase AC pumps
Cooled by the fuel

Question 6

How are fuel tanks pressurised

Answer 6

With ram air

Question 7

Fuel tank inerting

Answer 7

System to mitigate risk of inflammability of air fuel mixture in empty tanks

787 use nitrogen generators which fed into tank to fill void

Question 8

Piston Engine fuel types/properties/colour indication at pumps

Answer 8

AVGAS 100LL - Blue - 0.72
AVGAS 100 - Green - 0.72
MOGAS

Low flash point
Good lube properties
Non corrosive
Anti knock properties
Op across wide range of temps

Red background with white text

Question 9

Diesel Aero engines use/types and properties

Answer 9

Aviation kerosene

Jet A1 - 0.85SG - Additives - flash point 47 degrees
Jet A - 0.85SG - flash point 40 degrees
Jet B - 0.77SG - lowest flash point

Waxing of fuel around -60 degrees

Question 10

Waxing

Answer 10

Prone in turbine fuel systems
Waxy deposits as fuel does not freeze at one temperature
Starts around -40 degrees

Question 11

Cross-feed valve

Answer 11

Open cross feed valve to switch between tanks
Switch off tank with lower fuel
Switch on tank with higher fuel
Never switch off a tank without cross feed valve being open

Question 12

Large AC Fuel Systems have what pumps

Answer 12

Two electrically powered low pressure booster pumps
LP pumps supply fuel direct to the engine

Question 13

LP Booster Pumps - power source/pressure

Answer 13

Operate on 115v AC off different busbars
Pump pressure 20-50psi
Fuel pumps in centre tank fed at HP to ensure used first

Question 14

Bypass valve in booster pumps

Answer 14

Fitted downstream of LP pump to allow engines own high pressure pump to draw fuel directly from the tank if LP pump fails

Question 15

Jet Pump

Answer 15

In event of both LP pumps failing scavenge fuel from lowest part of tanks using Venturi effect

Question 16

Vent Surge

Answer 16

Collect fuel overflow and allow fuel to be drawn back to tank when over pressurise (has a limit will still spill over)

Question 17

Spar valve

Answer 17

Cut off fuel before it enter engine bay in emergency event such as fire

Question 18

FCOC

Answer 18

Used to prevent fuel waxing via heat exchanger of heating fuel and cooling the engine oil

Question 19

Resistive fuel gauge system

Answer 19

Uses variable resistor DC POWER
Measures volume/prone to errors due to flight
- different tank size/shape hard to calculate actual volume

Used on large ac

Question 20

Capacitance fuel gauge system

Answer 20

Low voltage cylindrical capacitor probe across tank with potential difference between them

System measure difference in dielectric of fuel and air to measure fuel level

+ failed probe will be discounted from calculation
+ second probe used to measure density
+ 99% accuracy
+ power failure will indicate low gauge reading

Question 21

Fuel Flow Indicators

Answer 21

Used to monitor engine performance
Fitted after engine shut off valve between fuel control unit and engine
Indicate high fuel burn etc

Question 22

Jettison Limit switch

Answer 22

Prevent dumping all fuel overboard
Is a low level float switch

Must be able to reduce to landing weight within fifteen minutes

Question 23

Large transport AC refuelling principals

Answer 23

Point under the wing
Max refuel pressure 50 PSI/minimum 5 PSI

Question 24

Why do crew monitor fuel tank temperatures

Answer 24

Ac must be operated with fuel tank temperatures within 5 degrees of fuel freezing point

Question 25

Vent space for each fuel tank as required by CS23/25 is

Answer 25

2% of tanks volume

Question 26

Flash point is defined as

Answer 26

The lowest temperature at which a volatile substance evaporates to form an ignitable mixture with air

Question 27

Collector Box

Answer 27

Located at the bottom of fuel tank
Valve prevents flow of fuel back to main tank so there is a constant flow of fuel when manoeuvring

Not at the lowest point to prevent sludge blocking flow

Question 28

Parts of ac fuel system include

Answer 28

Fuel density sensors
Collector tank
Fuel jettison system
Tank baffles
LP pump

Question 29

FCU is

Answer 29

Fuel metering device that regulated fuel flow to engine via pilots demands

Filters are usually located before FCU

Question 30

Flash point of JET A1

Answer 30

38 Degrees

Question 31

Jet B flash point

Answer 31

-60 degrees

Question 32

Drip Sticks

Answer 32

Visual means of determine fuel quantity in wing tank

Stick unlocked and lowered until fuel enters upper end of the stick and drop out of the lower end

Tables of capacities corrected for airplane attitude are found it ac documents

Question 33

Main purpose of the DC fuel pump

Answer 33

Supply fuel to the APU

Question 34

Drain Valve

Answer 34

Allows pilot to drain off any water from the fuel tanks

Also used for maintenance to drain fuel

Question 35

Failure of AC fuel pumps how does the engine continue to provide fuel

Answer 35

HP fuel pumps in engine continue to suck in fuel

Question 36

Feeder box

Answer 36

Two low pressure fuel pumps to provide uninterrupted desecrated supply of fuel to the engine driven pumps

X2 for continuous supply

Question 37

Trim fuel system

Answer 37

Located in the tail of the aeroplane and allow fuel to be moved about to change the CG of the aircraft

Place further set away from CG at the tail

Question 38

Vent Lines

Answer 38

Allow air into the fuel tank to replace the volume of fuel consumed by engine to equalise the pressure