Jeppesen Oral- Chapter 15 ( Aircraft Fuel Systems)

Question 1

What are two reasons Prist is added to the fuel that is used in a turbojet aircraft?

Answer 1

Prist is a biocidal agent that (1) kills the scum-forming bacteria in the fuel tank, and (2) acts as an antifreeze agent, lowering the freezing point of the entrained water that is released from the fuel.

Question 2

What are two types of fuel cells that are used in modern aircraft?

Answer 2

Integral fuel cells (cells that are a sealed-off portion of the structure) and bladder-type cells.

Question 3

Why are fuel tanks divided into compartments, or why are baffles installed in some tanks?

Answer 3

The compartments or baffles keep the fuel from surging back and forth as the aircraft changes attitude in flight.

Question 4

What is meant by an integral fuel cell?

Answer 4

A part of the structure in which all of the seams and joints are sealed so they will be fuel tight. The structure itself then becomes the fuel tank.

Question 5

Where are fuel system strainers located?

Answer 5

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.

Question 6

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.

Answer 6

Booster pumps are used to produce fuel pressure for starting the engine, to keep the fuel from vapor locking at high altitude, and to transfer fuel from one tank to another.

Question 7

What is meant by a compensated engine-riven fuel pump?

Answer 7

An engine-driven fuel pump whose pressure relief valve is acted upon by the pressure of the atmosphere. A compensated pump varies its outlet fuel pressure so that it will stay a constant amount higher than the pressure of the air that is entering the carburetor.

Question 8

Why do engine-driven fuel pumps have a bypass valve in them?

Answer 8

The bypass valve allows fuel from the booster pump to flow around the engine-driven pump mechanism for starting the engine and to supply the engine with fuel if the engine-driven pump should fail.

Question 9

Why must an aircraft duel valve have a detent in its operating mechanism?

Answer 9

The detent gives the pilot a positive indication by feel when the selector valve is in the full ON and full OFF position.

Question 10

What characteristic of the fuel is measured with the mass-flow fuel flowmeter that is used with turbine-engine aircraft?

Answer 10

The density of the fuel.

Question 11

What is used as a flowmeter for fuel-injected, horizontally opposed aircraft engine?

Answer 11

A pressure gage that measures the pressure drop across the injector nozzles in the engine.

Question 12

What is meant by a cross-feed system in an aircraft fuel system?

Answer 12

A cross-feed system allows fuel from any tank to flow into any engine.

Question 13

Why do some aircraft have provisions for jettisoning fuel in flight?

Answer 13

Aircraft that are certificated with a higher takeoff weight than their allowable landing weight must have provision for jettisoning fuel. This allows enough fuel to be dumped to bring the weight down to that allowed for landing in case an emergency occurs before this amount of fuel can be burned off.

Question 14

What is meant by a single-point fueling system?

Answer 14

A pressure fueling system in which the fuel is pumped into the aircraft through an underwing fueling port. The fuel flows into a manifold, and then into the correct fuel tank as selected at the fueling station.

Question 15

What gas is used to purge a fuel tank of all fuel vapors?

Answer 15

Carbon dioxide or nitrogen.

Question 16

Why do turbojet aircraft normally have fuel temperature indicators?

Answer 16

Because of the low temperatures at which these aircraft operate, it is possible for water to precipitate out of the fuel and freeze on the filters, shutting off fuel to the engines. The temperature can be kept ablove freezing by directing it through a fuel heater as needed.

Question 17

How is a fuel leak indicated on a reciprocating-engine-powered aircraft?

Answer 17

The dye that is in the gasoline stains the area around the leak.

Question 18

What is the purpose of a drip gage in the fuel tank of a large aircraft?

Answer 18

The drip gage allows a mechanic to check the fuel level in a tank from the bottom of the tank.

Question 19

What safety precautions should be taken before an aircraft is defueled?

Answer 19

Be sure that the fuel truck is properly located, the truck and the aircraft are electrically grounbded, all electrical power except that needed for the defueling operation is turned off, and the fuel is returned to the proper tank or other container.

Question 20

What markings must appear near the filler opening of the fuel tanks on reciprocating-engine-powered aircraft and on a turbine-powered aircraft?

Answer 20

On a reciprocating-engine-powered aircraft: The word FUEL and the minimum grade of fuel.
On a turbine-powered aircraft: THe word FUEL, the permissible fuel designations, the maximum permissible fueling supplu pressure, and the maximum permissible defueling pressure.

Question 21

Why do some aircraft have fuel jettison systems

Answer 21

To allow the crew to reduce the weight of the aircraft down to or below the maximum allowable landing weight.

Question 22

Is there any reason why a fuel jettison system might be required on a small aircraft?

Answer 22

Yes, if the maximum takeoff weight exceeds the maximum allowable landing weight, a jettison system would be required.

Question 23

What are some other names for a single-point fueling system?

Answer 23

An underwing or pressure fueling system.

Question 24

Why do multi-engine airplanes have fuel crossfeed systems?

Answer 24

To allow any engine to draw fuel from any tank.

Question 25

The fuel selector valve for a multi-engine airaft must have at least three positions. What are they?

Answer 25

ON, OFF, and Crossfeed

Question 26

Why do some fuel tanks have internal baffles?

Answer 26

To resist fuel surging or sloshing caused by changes in the attitude of the aircraft.

Question 27

What are the two types of fuel cells?

Answer 27

Integral or wet wing fuel cells, and bladder-type fuel cells.

Question 28

What does the term “wet wing” mean?

Answer 28

It means that sealed portions of the aircraft wing structure form the fuel tank(s)

Question 29

How is the weight of the fuel supported when bladder-type fuel cells are used?

Answer 29

The bladder is supported by the aircraft structure which contains it.

Question 30

Why do turbine-engine aircraft have fuel temperature indicating systems?

Answer 30

To allow the crew to determine if the fuel is cold enough to produce a danger of the formation of ice crystals.

Question 31

Name four types of fuel quantity gauging systems currently in use.

Answer 31

Sight gauges, mechanical, electric, and electronic

Question 32

Why are electronic (capacitance-type) fuel quantity indicating systems more accurate than other types?

Answer 32

They measure the mass of the fuel instead of the volume.

Question 33

What are drip gauges and sight gauges?

Answer 33

Underwing, bayonet-type fuel gauges.

Question 34

What is the purpose of an in-transit light associated with an electrically operated fuel tank shutoff valve?

Answer 34

To provide an indication that the valve is in motion between one positition and another.

Question 35

For what reason is a fuel jettison system usually divided into two separate, independent systems, one for each wing?

Answer 35

To help maintain lateral stability by jettisoning fuel from a heavy wing if necessary.

Question 36

What procedures should be followed regarding gaskets and seals when replacing fuel system components?

Answer 36

All old gaskets and seals should be replaced with new ones.

Question 37

Is it possible for a fuel system to develop a leak that has no visible evidence such as a stain or spot, and if so, how?

Answer 37

An internal component such as a valve could develop a leak.

Question 38

How is a fuel tank checked for leaks following a patch or welded repair?

Answer 38

The tank is slightly pressurized with air and the repaired area is leak-checked with a soap and water solution.

Question 39

Name some advantages of a single-point fueling system.

Answer 39

It reduces fueling time, reduces chances for contamination and fire, and eliminates damage to the aircraft skin.