11.10 FUEL SYSTEMS👌🏼 Flashcards
Where are fuel tanks located?
- wings
- fuselage centre
- some have tanks in horizontal stabiliser
(Known as auxiliary tanks)
What are trim tanks?
- storing fuel and used to also trim aircraft
What are fuel lines/fittings made from?
- rigid pipe - stainless steel/aluminium alloy (connected with MS or AN fitting)
- Hoses - synthetic rubber inside, braided stainless steel exterior
What else can further protect fuel lines/fittings?
- fire sleeve cover to protect from fire and abrasion
Explain what is done when a fuel line fitting is found to be leaking?
- torque if not correctly done
- if leak does not stop, depressurise fuel line, disconnect fitting, inspect and replace
What must be ensured when metal fuel lines are used on aircraft?
- electrically bonded and grounded to aircraft structure
What are the 2 basic types of fuel
- Reciprocating engine fuel (AVGAS)
- turbine engine fuel (jet fuel)
Explain AVGAS
- Reciprocating engine
- combustion releases energy in fuel which is converted into mechanical motion (piston engines)
What are the 3 basic turbine engine fuel?
- Jet A1
- Jet A
- Jet B
What is the advantage of Jet B fuel over Jet A
- Can handle colder conditions
- lower freezing point (-50*c)
What is the freezing point of Jet A and Jet A1 fuel
- Jet A -40*c
- Jet A1 -47*c
What colour are turbine fuels
- colourless or straw
What are the 3 types of aircraft fuel tanks
- Rigid removable fuel tanks
- Bladder fuel tanks
- Integral fuel tanks
Explain rigid removable fuel tanks?
- like a car
- tanks riveted or welded together (leakproof)
- Includes baffle plates
- must be secured to airframe
Explain bladder fuel tanks?
- reinforced flexible material
- does not require large opening
- should lie smooth and no wrinkles
- patch can be used to repair
Integral fuel tanks
- wings, fuselage to form a fuel tank
- fuel tank sealed with fuel resistant 2 part sealant
- fuel tanks in wings referred as ‘wet wings’
What prevents fuel from moving around the aircraft?
- baffles
What are baffle check valves
- allows fuel to move to the low inboard section of tank
- prevents outboard movement of fuel
Where are integral access panels located
- underside of wing
Main reason for Nitrogen generating system (NGS)?
- reducing risk of fuel explosion by replacing oxygen in fuel tanks with nitrogen
Explain how NGS (Nitrogen generating system work
- engine bleed air system
- oxygen, nitrogen and other gases is then cool
- goes into ASM (air separation module)
- oxygen is vented out the system
- nitrogen en-riched air is put into fuel tank
Can nitrogen in a fuel tank cause combustions?
No
When is low flow mode activated for On Board Inert Gas Genration System?
- when air pressure is low (cruising conditions)
When would On Board Inert Gas Generation System go in high flow mode?
- when air pressure rises
- pumping nitrogen at faster rate as more oxygen is subjected
How much maximum oxygen content is allowed to be maintained on landing?
- 12%
What are the 4 fuel leak classification?
- stain
- seep
- heavy seep
- running leak
What do you do to find out what classification of fuel leak has occurred?
- clean surface and wait 30mins
Explain SFAR 88
- requires permanent safety of fuel tanks
- special inspections and maintenance procedures
Explain Critical design control configuration (CDCCL) ?
- features in aircraft must be maintained during repair, mods etc
- why is fuel venting important before maintenance is carried out
- vapour concentration must be below lower explosive limit
- must have adequate oxygen level inside tank
- fuel tank must be ‘safe’ before entering
- why is fuel venting important before maintenance is carried out
- vapour concentration must be below lower explosive limit
- must have adequate oxygen level inside tank
- fuel tank must be ‘safe’ before entering
What are gas detectors
- measure concentration of combustible vapours
- alarm when it’s raised to explosive hazard levels
What are gas detectors
- measure concentration of combustible vapours
- alarm when it’s raised to explosive hazard levels
What are the 3 fuel supply systems
- gravity feed
- pressure feed
- injection feed
Explain gravity fuel feed system
- gravity needed to supply fuel to engine
- usually high wing aircraft
Explain pressure fuel feed system
- engine driven/electric pump must be used
Explain injection fuel feed system
- gravity + fuel pump
Explain hand operated fuel pumps
- manual pump (continuous delivery)
- con = requires fuel line in flight deck
Explain vane-type fuel pumps
- constant displacement pump moving constant volume of fuel with each revolution
- electric motor rotates pump shaft
- engine driven = driven by accessory gearbox
- excess pressure goes into outlet valve and the rest comes back to inlet
Explain centrifugal pumps
- usually electric and submerged in fuel tank or located outside of the bottom of the tank, with inlet of pump extending into tank
- ensures positive pressure
- shut off valve - so pump can be replaced without draining tank
Explain ejector pumps
- used to always maintain a fuel supply
- fuel flow inboard towards the fuel pumps
What are the 3 common fuel filters?
- micron filter
- wafer screen filter
- plain screen mesh filter
Which filter has the greatest filtering action
Micron filter
Explain dumping/Jettison
- system that allows flight crew to dump fuel overboard
- Jettison lines shared with refuelling manifold
- jettison switches are usually guarded
Why are fuel vents designed
- prevent build up of pressure in fuel tank
What are surge tanks
Designed to contain fuel overflow and prevent spillage
What are vent float valves
- fuel is low = valve open (float keeps valve open)
- fuel is high = valve closed (float rises)
What are flapper valves
- prevent fuel from travelling outboard during manoeuvres
- allow fuel to drain inboard during operation
What is the purpose of draining
- drain water from fuel tank
- drain fuel for maintenance
Explain manual drainage
- consists of valve piston and internal check valve
- closed by springs
- pressure onto check valve opens and liquid can be drained
What does the fuel cross feed valve allow
- flow between left and right engine fuel feed manifolds
- one/two fuel tanks can supply both engines
What does the fuel entry coupling incorporate
- spring loaded check valve preventing fuel leaks
What are the 3 refuelling methods
- manual
- automatic
- override
2 methods of defuelling
- pressure defuelling
- suction defuelling
Explain pressure defuelling
- boost pumps used
- pump feeds, fuel feed manifold to the defuel valve
Explain suction defuelling
- fuel truck used
- manual defuel valve must be open during suction
- if crossfeed valve is open, fuel is driven out of both tanks
- takes longer time than pressure defuelling
- can be done without aircraft power
What is used to compensate for CG change in the air
- THS fuel tank to balance aircraft as CG moves
- simply a transfer of fuel between tanks
