11.10 Fuel Systems Flashcards
What ATA chapter is Fuel Systems
ATA 28
What type of fuel are turbine engine fuels
Kerosine type fuels, similar to diesel
What are the 4 most common fuel types used on modern aircraft
- Jet A
- Jet A1
- Jet B
- JP5
What is the most common fuel for jet aircraft in Europe
Jet A1
What makes Jet A1 reasonably safe to handle
It has a high flash point and a low freezing point
What is the flash point and freezing point of Jet A1 Fuel
Flash point = +38 Celsius
Freezing point = -47 Celsius
What is Jet B Fuel usually used for
Military aircraft
What are the main requirements for turbine fuels
- A low freezing point and a low enough flash point to have good ignition capabilities but still safe enough for handling
- A low tendency to vaporise at high altitude
What is the required minimum freezing point for turbine fuel
At least -40 Celsius
What is the flash point of a fuel
Lowest temperature which a fuel creates enough vapours to build a fuel/air mix to be ignited
Why is high volatility of fuel an advantage
- Desirable for engine starts in cold weather
- Eliminate vapour lock
- Reduce fuel loss due to vaporisation
What is the density of Jet A1 and Jet A fuel
They are the same at 0.81kg/ltr at a temperature of 15 Celsius
What are the two ways fuel carries water
- Can dissolve in fuel
- can settle on fuel
It is generally visible as small bubbles or water droplets
What is the most common way to test for dissolved water in fuel
A syringe of fuel is taken and chemically tested
What does the fuel storage system consist of
Fuel tanks, the tank drain system and the tank vent system
What is the purpose of surge tanks
To ensure the tanks are properly ventilated
What are the most common types of tank on modern aircraft
Integral tanks
What is used in fuel tanks to dampen the effect of fuel sloshing around
Ribs in the wing and non sealed divider walls in the centre tank
What type of valve is used to prevent the fuel boost pumps from running dry
Flap baffle check valve
What is done to fuel tanks in critical areas as a safety precaution
They are ventilated by passing air around the fuel tank and then releasing the air into the atmosphere carrying away fuel leaks and vapours
How is the stabiliser tank ventilated
With RAM air
What is use to indicate if there has been a fuel leak
A leak monitor
It is a spur pipe connected to the drain valve
Where are drain valves located on fuel tanks
The bottom
What are the 2 types of drain valve
Direct drain valve and indirect drain valve
How are drain valves operated
For safety reasons they are usually operated manually
If they are in a hard to reach place they can be operated electrically
Where would water scavage systems be used
In large fuel tanks where large amounts of water would be expected
How do the water scavage systems remove water from the tanks
By the means of the tank boost pumps, most of the water will get mixed with the fuel and go to the engines and the remainder will go to the jet pump
How is fuel normally removed from a tank
By gravity
What is the purpose of the fuel tank vent system
To protect tanks against overpressure and negative pressure
What would be found inside the vent surge tank
The NACA intake and overpressure relief valves
What is the purpose of the NACA ducts during flight
They draw in air and the air acts as a cushion on the fuel which reduces vaporisation
What happens if dangerous levels of pressure occur in fuel tanks
Pressure release valves open to prevent structural damage
What are the two types of fuel tank pressure relief valve
Spring type or carbon disk
What does the refuelling system consist of on an aircraft
Pipes, valves controls and indicators
What are the two methods of fuelling
Pressure and gravity
What functions can be had on a refuelling panel.
Refuelling and defuelling and manual transfer of fuel between the tanks
What is the biggest disadvantage of gravity fuelling
The long time it takes to fuel
When pressure fuelling what pressure would fuel be pumped at
50PSI
What is the refuelling manifold
A long pipe which connects all of the tanks
What are the 3 modes of pressure re fuelling
Manual, automatic and override
If in manual refuelling mode what must be done prior to refuelling
You must calculate the fuel distribution
When is the override fuelling mode used
If electrical power to the refuelling valves is not available
What unit is fuel usually indicated in on a refuelling panel
In kilograms
Where does normal refuelling power come from
Ground power or APU
Alternatively the battery can be used
What are volumetric top-off systems used for
They are a failsafe to prevent tanks from being overfilled. Ones the tank is full they will cut the power to the tank valve
Alternatively high level sensors are installed
What do the refuelling couplings incorporate
Spring loaded check valves which prevent fuel leaks
During flight which tank empties first
The centre tank
What are solenoid operated refuelling valves used for
Fail safe
What is a diffuser
The diffuser is made up of a perforated tube that allows fuel to exit the manifold. The baffle on top of the diffuser direct the fuel flow downwards
What can diffusers also be called
Distribution manifolds
What is the main purpose of the fuel feed system
Ensure proper fuel supply to engines and APU
How many boost pumps must there be for each consumer in the fuel feed system
2
What are fuel scavage systems used for
To reduce the amount of non usable fuel in fuel tanks
What are the 3 methods of fuel management
- Through pressure. Some pumps will be pumping at a higher rate than other to empty that tank first
- Another is computer controlled (modern aircraft)
- The last is pressure and computer controlled
Where are the controls for the fuel feed system found?
The centre overhead panel for easy operation for the pilot
Where the controls for the fuel feed shut off valves found
On the engine fire panel
How is fuel feed managed on modern aircraft
It is done automatically, done by pressure/ electronically controlled
What are the two methods of pressure controlled fuel feed
- high pressure pumps
- Sequence valve
What are the two different types of fuel boost pumps used on aircraft
High and low pressure
On aircraft using the same type of boost pump in the same tank what would be used to give different output pressure
Pressure reducing devices
What are high pressure output pumps also called
Override and jettison pumps
They deliver twice as much pressure as standard pumps
What are sequence valves used for
They are installed on the pump outlets of some of the standard boost pumps and reduce their output pressure
In the taxing phase (first phase) what tank feeds all engines
The centre tank
The second flight phase is take off, what happens to fuel delivery at this point
As the flaps come down on take off this initiates the second phase of flight and the boost pumps go from being on standby to on and each engine is supplied from an individual tank
When is cruise feed activated?
When take off has completed and the flaps have been retracted
During the cruise feed stage what fuel pumps are suppling the engines
The double capacity override and jettison pumps
Why is fuel transfer in flight limited
As it would have an effect of the centre of gravity
How many transfer valves are in each tanks
There are 2 for safety reasons both with independent power supply
What is the most common method of fuel scavage system
Jet pumps
What is the second most common way of fuel scavenging
Electrically driven scavage pumps
What is the fuel used to cool on the aircraft
The engine oil and through bypass valve to the IDG
Where are the fuel boost pumps found?
Outside of the tank on the front or rear spars or found in explosion proof canisters inside the tank
What do pumps generally consist of
They are mostly impeller type pumps and consist of an AC motor that drives the impeller
How is it possible to remove fuel boost pumps from their canisters whilst the fuel tank is still full?
A special removal valve is used which shuts off the fuel inlet as the pump is pulled out of the canister
What are the two methods of defuelling an aircraft
- Pressure defuelling
- Suction defuelling
What type of pressure do the boost pumps run at on defuelling
25-50 psi
What is the preferred method of defuelling an aircraft
Pressure defuelling
What is the minimum suction required for defuelling
10-15psi
What is 1 major disadvantage of suction defuelling
It is difficult to defuel 1 tank and not the other
What components are used during fuel transfer
- Fuel boost pumps
- Fuel feed manifold
- Defuelling or defuel transfer valve
- The refuelling manifold
Can defuelling be done in automatic or manual mode
MANUAL mode only
How is fuel saved due to the trim tank system
As the trim tank reduces aerodynamic drag in flight
How is the aircrafts actual centre of gravity determined
The manufacturer determines the actual centre of gravity
Loading and refuelling however affects centre of gravity
For safety reasons what calculates the centre of gravity
The Flight Management Computer (FMC)
For additional safety reasons where would you find the target centre of gravity
Approx 2% forward of the certified aft limit of the aircraft
What is the fuel jettison system used for
It allows the pilot to dump fuel prior to landing to prevent a heavy landing
What are the main components in the jettison pumps
Fuel boost pumps or special jettison boost pumps
What do the jettison nozzles ensure when fuel dumping
That the fuel remains in a non vaporised compact flow so it drops quickly away from the aircraft
What are the special jettison nozzles called
Anti corona outlets
What safety precautions are in place to prevent accidental fuel dumping through the jettison system
There are switches on the overhead fuel panel to first arm the jet pumps and separate ones to commence fuel dumping
What main safety feature is adopted when installing fuel jettison pump inlets in fuel tanks
The inlets are installed above the floor of the tank so there will always be an amount of fuel left in the tanks and the pumps will continue to jet fuel until the pumps run dry
What are the Boeing and Airbus systems used for fuel monitoring
ECAM and EICAS pages
How is fuel quantity indicated (units)
In mass i.e kilograms or tons
What are the main features of fuel quantity probes in a fuel tank
The amount of probes vary in size and quantity depending on the size and shape of the tank. The probes are installed vertically and reach from the top to the bottom of the tank
What do the fuel quantity probes consist of
- Two thin walled aluminium alloy tubes
- Installed coaxially and electrically isolated from each other to form a capacitor
- Each probe also consists of a terminal block which contains the electrical connection and the mounting brackets which fix the probe to the tank
Can the fuel quantity computer calculate the fuel levels of 1 probe is faulty
Yes
In order to calculate the fuel mass of a tank very accurately the computer needs additional information to the information given from the probes, what is this
The density and dielectric constant of the fuel
This is given by the fuel characteristic sensors
What are the two fuel characteristic sensors called in each tank and what is the location on the sensors in the tank
A Compensator and a Densitometer
They are located in the bottom of the tank so that they are covered in fuel for as long as possible
What does the densitometer measure
The density of the fuel
As a percentage what is the fuel accuracy usually
Typically over 99%
What are 3 widely used examples of fuel level sensor
- A float switch
- Thermistor type sensor
- Single point sensor
How does the thermistor type fuel sensor work
Uses the thermal conductivity of fuel and air to detect the fuel level
What is used to measure fuel temperature
A thermistor is used to measure fuel temperature
How would you measure the fuel quantity or levels with out using the electrical sensors
Measuring sticks or drop sticks and magnetic level indicators
What are the 3 main methods of determining aircraft attitude on the ground?
- The inclinometer method
- The plumb method
- The attitude monitor method
How does the inclinometer attitude detector work
Essentially like a spirit level
How does the plumb attitude method work
A plumb is attached on the wheel well and a measurement is taken from the scale
What 4 main things would you need to know when taking a manual fuel reading
- The aircraft attitude
- The measuring stick number
- Stick reading
- The fuel density checked with a hydrometer
What 3 categories are there for fuel handling safety procedures
- Fire prevention
- Fire extinguishing
- Personnel safety
What is one main maintenance task never to be carried out during refuelling
Topping up of oxygen bottles
What are the two main personnel hazards with working with fuels
Vapour inhalation and fuel on skin
What heat sources may inflame a fuel/air mixture
- Electric switching
- HF transmission
- Weather radar operation
- By metal parts like tools being stuck together
- By electric static discharge
NOTE: During refuelling an electric static charge is created
When entering fuel tanks what is the clothing made from that you are required to wear
Cotton
How many people are required minimum for fuel tank entry
Minimum 2 or more
What are the 3 categories of fuel tank entry
Cat 1 - Has a direct access door, access by head and shoulders only
Cat 2 - Has direct access and wide enough to fit entire body
Cat 3 - No direct external access door, but there are internal openings which allow you to get in and wide enough for rescue if necessary
What are the two tests that must be performed before automatic refuelling commences to ensure the system is operating correctly
- The quantity indicator test
- High level test
