J. Aircraft Fuel Systems
After welding an aluminum fuel tank, to what pressure should the tank be tested? (AM.II.J.K3)
3.5 psi.
Why is a fuel jettisoning or dump system required for some aircraft? (AM.II.J.K6)
A fuel dump system is installed on most large aircraft and allows the flight crew to jettison, or dump, fuel to lower the gross weight of the aircraft to its allowable landing weight.
What is used as a sensor in the fuel tank for the older resistance-type fuel quantity indicating system? (AM.II.J.K9)
A variable resistor with an arm that is moved by a float riding on top of the fuel in the tank.
What types of operations are fuel systems designed and certified for? (AM.II.J.K1)
Any maneuver or operating condition for which the aircraft is certified.
What problem can occur in a bladder tank with a blocked vent? (AM.II.J.K3)
As internal tank pressure decreases, the pressure differential between the atmosphere and the tank can cause the tank restraints to fail and the tank can collapse and block the fuel outlet.
What color is grade 100-LL fuel? (AM.II.J.K7)
Blue.
What are the three different types of fuel tanks? (AM.II.J.K3)
Built-up tanks, integral tanks, and bladder tanks.
When must the fuel quantity indicating system indicate "zero?" (AM.II.J.K9)
During level flight when the fuel in the tank is equal to the unusable fuel supply.
To what fuel flow is an aircraft fuel system designed for? (AM.II.J.K4)
Each fuel system must be constructed and arranged to ensure fuel flow at a rate and pressure established for proper engine and auxiliary power unit (APU) functioning under each likely operating condition.
Where can you find the correct part number for the fuel quantity sensor to be installed in an aircraft fuel tank? (AM.II.J.K2)
In the Illustrated Parts Catalog for the aircraft.
What are two types of fuel cells used in modern aircraft? (AM.II.J.K1)
Integral fuel cells (cells that are a sealed-off portion of the structure), and bladder-type cells.
How can you detect jet fuel in the sample taken from the tank sump drains? (AM.II.J.K7)
Jet fuel is basically clear and it has an odor similar to kerosine.
Is the procedure of draining the sumps with the aircraft in the ground attitude an assurance that all of the water is removed from the tanks? (AM.II.J.K5)
No; some aircraft require special procedures to remove all of the water. Refer to the airplane flight manual or pilot's operating handbook.
What markings must appear near the filler opening of the fuel tanks on a reciprocating-engine-powered aircraft, and on a turbine-powered aircraft? (AM.II.J.K5)
On a reciprocating engine powered-aircraft: the word "Avgas" and the minimum grade of fuel. On a turbine engine powered aircraft: the words "Jet Fuel," the permissible fuel designations, the maximum permissible fueling supply pressure, and the maximum permissible defueling pressure.
Where are fuel system strainers located? (AM.II.J.K2)
One strainer is located in the outlet to the tank, and the main strainer is located in the fuel line between the outlet of the fuel tank and the inlet to the fuel metering device.
How do you prepare an aluminum fuel tank for welding? (AM.II.J.K3)
Remove all fuel and thoroughly wash the tank, inside and out, with hot water and detergent. The tank should be purged with live steam for at least 30 minutes to remove all residual fuel and vapors.
Why do the fuel strainers used on some turbine-engine aircraft have a warning device that signals the flight crew when the strainer is beginning to clog up? (AM.II.J.K2)
Strainers clog because ice forms on the filter element. The flight crew can route the fuel through a fuel heater to melt the ice.
Why are fuel tanks divided into compartments or have baffles installed in them? (AM.II.J.K3)
The compartments or baffles keep the fuel from surging back and forth as the aircraft changes its attitude in flight.
Why must an aircraft fuel valve have a detent in its operating mechanism? (AM.II.J.K2)
The detent gives the pilot a positive indication by feel when the selector valve is in the full ON and full OFF position.
What is the purpose of a drip gauge in the fuel tank of a large aircraft? (AM.II.J.K9)
The drip gauge allows a mechanic to check the fuel level in a tank from the bottom of the tank.
How is a fuel leak indicated on a reciprocating-engine-powered aircraft? (AM.II.J.K3)
The dye in the gasoline stains the area around the leak.
What must be done after a fuel valve is replaced? (AM.II.J.K2)
The fuel system must be checked for leaks.
What must be done if the sump drains sample shows traces of jet fuel? (AM.II.J.K8)
The fuel system must be drained and flushed out with the proper grade of aviation gasoline.
What is the function of the sump in a fuel tank? (AM.II.J.K3)
The sump, or lowest point, in a fuel tank is located below the fuel outlet. The sump collects water and contaminants and will have a drain to remove them.
What must be done after a fuel system strainer has been cleaned or replaced? (AM.II.J.K8)
The system must be tested for leaks by pressurizing the system with the boost pump, if one is used.
What must be done before a fuel selector valve can be removed from an aircraft? (AM.II.J.K2)
The tank to which the valve is connected must be drained or otherwise isolated.
What is the principle upon which the electronic-type fuel quantity indicating system operates? (AM.II.J.K9)
Tubular capacitors extending across the fuel tanks change their capacitance as the fuel level changes. The dielectric constant (k) of the fuel is approximately twice that of air.
What is used as the sensor in the fuel tank for an electronic-type fuel quantity indicating system? (AM.II.J.K9)
Tubular capacitors that extend across the fuel tank from top to bottom.
How does water appear in the fuel drained from the tank sumps? (AM.II.J.K2)
Water appears as a clear globule in the bottom of the container used to collect the fuel drained from the sumps.
Why is it important to drain all of the fuel sumps before the first flight of the day? (AM.II.J.K5)
Water can condense in the fuel tanks and it must be drained out before the aircraft is safe for flight.
