11.10 Flashcards
Why do fuel tanks have a sump
A sump is below where fuel is pumped to the engines this is because water and other contaminants may settle here as water is denser than fuel.
What type of engines use AVGAS
Reciprocating engines.
Turbine engine fuel types
Jet fuel is a kerosine type with a high flash point making it less flammable.
Jet A1, A and B
Most popular is A1
Jetb is used in colder climates due to its higher volatility.
Jet A/A1 have the same density of 0.81kg/L at 15 degrees C
Fuel colour code
AVGAS 100LL is mainly used in the US and is dyed blue.
Some 100/130 octane fuels are still available - dyed green.
82UL is dyed purple.
AVTUR is colourless or straw
Ridged / removable fuel tanks.
Made with 3003 or 5052 aluminium or steel.
Easy to remove,repair,replace if there is a leak.
Nitrogen generating system
Improves safety by replacing the oxygen in fuel tanks with nitrogen which reduces the chance of fires and explosions.
How does NGS work
Removes oxygen from the bleed air to generate nitrogen.
The air separation module separates them based on the different molecular sizes and diffusion rates.
O2 is more permeable and smaller.
NGS
Nitrogen is continually pumped into tanks, pressure valves regulate flow so tank is not overfilled.
Low or high modes.
Low mode conserves bleed air.
During cruise and climb it is in low mode
During descent it is in high flow mode so O2 content does not go over 12%.
Fuel leak classifications
Stain
Seep
Heavy seep
Running leak.
30 mins to monitor leak to classify it.
SFAR 88
Requires permanent safety of fuel tanks.
Requires introduction of maintenance procedures.
Mainly following crash of TWA flight 800
CDCCl
Refers to fuel systems design which must be maintained to ensure unsafe conditions do not develop.
Items included need to be kept as designed to maintain safety.
CDCCLs are mandatory.
Items include:
- bonding leads
- FQI harnesses and probes
- fuel pumps.
- wing access doors.
Ignition of fuel vapours.
Wiring is immersed in fuel.
Risk comes from electrical arcs, heating, friction sparks, hot surface ignition.
Conditions to ignite fuel vary with pressure / temp. And can be affected by fuel movement.
Fuel tank entry and closure.
Concentration of vapours must be kept below lower explosive limit.
Continual venting of tanks.
Atmosphere of tanks needs to be constantly monitored
It’s a team task, everyone should be qualified and each person should have a respirator
Fuel tank closure
Prior to closure make sure no items were left inside.
Gravity fuel feed system
Use gravity to supply engine
High wing a/c are most common.
Pressure fuel feed system
An engine driven / electric pump used.
Electric pump used to supply pressure to start engine. And as a backup in case one fails.
Injection fuel feed system.
Jet a/c fuel feed system.
Hand pump (fuel)
Little can go wrong but fuel is pumped to flight deck
Old planes.
Vanetype pump (fuel)
Driven by accessory gear box some have adjustable pressure relief.
Centrifugal pump (fuel)
Most common type of pump
Variable displacement pump
Ejector pumps.
Fuel tanks with inbuilt fuel pumps are built to maintain a fuel supply to the pump inlet, so the pump does not cavitation and is cooled by the fuel.
Fuel is directed through a venturi.
Water in the fuel is mixed with fuel so it does not impact he engine.
Fuel filter type
Micron filter waferscreen mesh, a plain screen mesh.
Fuel dumping/jettison
Jettison lines are often shared with refuel lines.
Jettison switches are guarded.
Fuel vent systems
prevent the build up of pressure in the fuel tanks and allow proper flow of fuel.
Surge tanks
Found on large a/c. Similar construction to integral fuel tanks.
Contain fuel overflow and prevent fuel spillage.
Not used for fuel storage.
Fuel drain valves.
Purpose is to drain fuel from the system.
Water must be drained during scheduled maintenance.
Also provides access to the fuel tanks and allow for maintenance.
