Module 11.10 Fuel systems Flashcards
All fuel tanks have a sump and a drain at the lowest point of the tank for what purpose?
To allow contaminants and water to settle
What is the purpose baffle in all tanks except the smallest?
To prevent fuel surges when the Aircraft is manoeuvred
What is provided in the fuel tanks to allow from volume increase with temp?
Expansion space
What are jettison valves?
Valves that allow the fuel to be jettisoned to reduce weight to the correct landing weight
What are trim tanks?
They store fuel and trim the aircraft
i.e. THS
What is the purpose of cavities in the wing tips?
Vent/surge tanks ensure fuel tanks are properly vented to remove vapours
How can mach tuck be corrected using fuel?
Move fuel from forward to aft tank, CoG moves back at the same rate as the CoP
Depending on location and application fuel lines can be what?
- Rigid
- Flexible
What is an additional use of fuel in the engine?
Cooling of IDG oil
Where would CRES lines be used?
Engines, wheel wells, any areas susceptible to high temp, abrasion and debris
What are rigid lines made from?
Aluminium alloy or CRES
What may be added on top of rigid and flexible fuel lines for extra protection?
Fire sleeve (corner held on with steel clamps)
What must be done to all fuel lines?
Bonded and grounded
If a leak is detected on a fitting, what should be done?
Re-torque the fitting, don’t over torque
What fuel do reciprocating engines use?
AvGas
What are the 3 jet fuel types?
- Jet A
- Jet A1
- Jet B
Can AvGas and jet fuel be mixed?
No they can’t
How are different types of fuel distinguished?
Fuel colour coding:
- AvGas purple
- Jet A colourless or straw
Why may jet B be used, but what is the drawback to use?
Lowest freezing point -50C
But it is more volatile
What are the 3 types of fuel tank?
- Rigid removable
- Bladder
- Integral
What are rigid fuel tanks made from?
3003 or 5052 aluminium alloy or CRES
How are seams sealed to prevent leaks?
- Riveted
- Welded
To minimise vaporisation what should be done to the fuel?
Pressurised
How should bladder tanks be installed into the structural bay or cavity?
Smooth without wrinkles
Bladder tanks may sit on raised internal structures like ribs or frames, what is used to support the tank?
Fibreglass planks to prevent chaffing
What is another material that may be used for rigid?
Terneplate
Where are seams on a bladder tank?
Around installed features like valves, drains, vents
How may a leak be repaired in a bladder tank?
Apply a patch
What are integral fuel tanks?
Fuel tanks that use the structure or fuselage of the aircraft for fuel storage
What is the benefit to integral fuel tanks?
- Reduced weight
- High volume
Aircraft with wing tanks are commonly referred to have what?
Wet wings
What is the purpose of baffle check valves?
To allow fuel to move from outboard to inboard, but not inboard to outboard
What is the purpose of integral fuel tank access panel?
Allow for inspection and maintenance
What are aluminium panels sealed in place with?
O-rings and an aluminium braided gasket
What is the purpose of the aluminium gasket?
Electrostatic bonding
What does SFAR88 require?
Permanent fuel tank safety requiring the inspection of the designed fuel systems and components
What does a Critical Design Control Configuration Limitations (CDCCL) include?
All information necessary to ensure the safety of fuel tank systems
What is the NGS?
Nitrogen generation system, improves fuel tank safety by replacing oxygen in tanks with nitrogen.
Inert Gas System
How does the NGS work?
Produce Nitrogen Enriched Air (NEA) by taking bleed air and filtering out oxygen in the Air Separation Module (ASM)
What is done with the oxygen after it is separated by the hollow fibres in the ASM?
Vented overboard
Where is the access to wing boxes?
Rear spars
Why is there a need for nitrogen to be constantly fed into the fuel tanks?
Displace air that enters to equalise the pressure between the fuel tanks and the ambient
What two modes does the IGS operate in?
- Low flow
- high flow
What are the 4 leak classifications?
1 - Stain
2 - Seep
3 - Heavy seep
4 - Running leak
How long is needed to monitor a leak?
30 mins
What are some examples of items that are part of the CDCCL?
- Bonding leads
- FQI harness and probes
- In tank harness routing
- Fuel pumps
- Wing access doors
Can CDCCL items be changed?
No they can not
What is a CDCCL feature of fuel pumps?
They stop pumping if the fuel level is too low
What are the requirements prior to fuel tank entry?
- Drained
- Vapours purged
- Breathing apparatus
- Safety person outside
Fuel tanks should be vented to ensure the concentration of fuel tank vapours are below what level?
Lower Explosive Limit (LEL)
What is the hazard level in regards to fuel vapour concentration?
When the vapour levels are between LEL and the Upper Explosive Limit (UEL)
What are the types of fuel supply?
- Gravity
- Pressurised
- Injection
In gravity refuelling the tanks are vented to the outside and each other, for what purpose?
To maintain equal pressure
What aircraft can’t use gravity fuel feed?
- Low wing level
To get adequate fuel pressure what is used?
Engine and/or electrically driven pumps
When may pressure fuel feeding be used?
- Fuel tank to far from engine
- Fuel tank too low
- Fuel flow rate too high
What is the injection fuel feed system?
Combines gravity and pressure fuel feed systems
What is the disadvantage to hand operated pumps?
Requires fuel to be routed through the flight deck
The wobble/hand pump is what type of pump?
Double acting, delivers on forward and back stroke.
Vane type
Vane type pumps are used for what purpose in piston aircraft?
Used as engine driven primary fuel pumps and auxiliary or boost pumps
Vane type pumps are what type of displacement?
Constant displacement/delivery
Unnecessary pressure build up can be relieved by what?
- Adjustable pressure relief
- Different pump
- Centrifugal
Constant displacement pumps can cause what issue?
Pressure build up
Where can centrifugal pumps be installed? (what extra items may be needed)
- Inside the fuel tank
- Outside the tank: it needs a pump removal valve to stop fuel spill when remove pumps
What type of displacement is a centrifugal pump?
Variable
Pumps in the tank require what?
Explosion/fuel proof housing. Canister
Inlet tube can have what so that when the pump is replaced there is no need to drain the tanks?
Shut-off valve
What is the most common type of pump in aircraft?
Centrifugal pump
What is the purpose of an ejector/jet pump?
Assist in ensuring that there is always fuel at the inlet of the booster pump
Where would the suction port be placed?
In the centre tank and/or the outboard tanks
Motive flow is taken from what tank to draw fuel from the outboard and centre wing tanks?
Wing tank in the Collector cell
How are fuel tanks designed with respect to pumps?
They are designed to ensure that there is always a fuel supply at the pump inlet
Where are fuel pumps in a fuel tank?
In an area called the collector cell
Ejector/jet pump are used for what reason in the collector cell?
To provide enough fuel to the pumps
Where is motive flow taken from?
The booster pump
What pump type has no moving parts?
Jet/ejector pump
What can an ejector pump not operate without?
Booster pump
What is required at the tank outlet/pump inlet?
Filtration screen
What are surge tanks?
Normally empty tanks that are designed to contain fuel overflow
What is the purpose of venting?
- Outward, equalise pressure with outside
- Inward, venting replace fuel with air to prevent negative pressure
Where is a vent float valve installed?
In the vent system
What position would the float be in if there is low fuel?
Fully open
What do flapper valves do?
Allow fuel to travel outboard to inboard through baffles in wings, but not inboard to outboard
Manually operated drain valves consist of a piston and check valve, what are these closed by?
Springs
How do you operate the drain valve?
Drain tool inserted, pressure applied. Piston moved into check valve opening it draining it.
How do you know when to stop draining?
When there is a smell of fuel
What happens to the centre of gravity during flight?
It moves around
How can the CoG be controlled to ensure that it remains within limits?
By moving fuel from the centre and wing tanks to the aft trim tanks. Vice versa
Transfer from centre to trim tanks is called what?
Aft transfer
What happens to the aft limit during flight?
It moves as the weight of the aircraft drops
How is CoG given?
As a percentage of Mean Aerodynamic Chord (MAC)
What type of pump is a centrifugal pump?
Non-positive
What are the three outputs of booster pumps?
- Engine feed
- Ejector pump motive flow
- Wing to centre transfers
Where do the booster pumps feed fuel to?
Engine feed manifold
What would the fuel tanker be connected to?
Refuel/Defuel coupling which is connected to the Refuel/Defuel manifold
Branches extend from the Refuel/Defuel manifold these deposit fuel into the tanks, what control this movement?
Tank inlet valve
When would the cross-feed valves be used?
Fuel imbalance, it is not a transfer of fuel but used to provide positive fuel feed to the engine
Under normal circumstances would cross-feed be used?
No it wouldn’t be
What are the 2 types of fuel transfer?
- In flight
- Ground
If there is a loss of electrical power the cross feed valve can be moved by what?
A manual override
Why is there a connection between the engine feed gallery and the refuel/defuel gallery?
For fuel transfer:
- Wings to centre
- Centre to wings
What is jettisoning?
Discarding of fuel overboard to get the aircraft below the Max Landing Weight (MLW)
To save weight jettison lines are often shared with what?
Refuel/defuel lines
Why is fuel jettisoned?
To get the aircrafts weight below the MLW
Why are jettison valves buttons usually guarded?
To prevent accidental operation
How is the jettison system designed?
Designed so that there is no chance of accidentally empty all fuel. This may be done by not all tanks have a jettison connection
What must be done before the refuelling is commenced?
Grounding and bonding
What should be tested before refuelling?
The tank inlet valves
What are the 3 modes of pressure refuelling?
- Manual
- Automatic
- Override
What is auto refuelling controlled by?
An onboard computer
When connecting the refuel nozzle what does the plunger do?
Raises the check valve to allow fuel to enter
When would override mode be used?
When there is no electrical power to the refuelling valves
Pressure defueling utilises what pumps?
Boosters
Does gravity defuelling exist?
No!
What is the disadvantage of suction defuelling?
- Takes longer
- Not all tanks can do it
- Empties all tanks at the same time
How is the information about fuel quantity given?
Fuel gauges
How are variable capacitance transmitters installed?
In fuel tanks and go from top to bottom. Also called probes
How does a ratiometer type fuel level indicator work?
Movement of a float
What is the purpose of the compensator?
Modifies the current flow to reflect temp variation which affects density
What are types of mechanical indicators?
- Dipstick
- Dripstick
- Magnetic level indicators
Where is the ultrasonic level sensor mounted?
On the top skin
Other than fuel quantity what is measured in the tank?
Temperature
How may low fuel temperature be rectified?
Fuel heater
Monitoring fuel pressure gives the flight crew what?
Early indication of a fuel system malfunction
During suction defuelling what provides the suction pressure?
The fuel truck
