Questions - Aircraft Fuel Systems

Study Aid Questions

Fill in the Blanks

1. Fuel with low volatility could cause __________, __________, and __________ acceleration.

2. Gasoline must truly burn rather than __________ or __________ .

3. Vapor lock is a condition in which AVGAS __________ in a fuel line or other component between the fuel tank and the __________.

4. Carburetor icing is most common at ambient temperatures of __________ but can occur at much higher temperatures especially in __________ conditions.

5. Detonation is the rapid, uncontrolled __________ of fuel due to high __________ , and __________ .
6. Turbine engine fuels have __________ volatility and __________ boiling points than gasoline.

7. Large transport category aircraft use often three types of fuel tanks. They are:
__________, __________, __________.

8. There are three types of aircraft fuel tanks: They are:
__________, __________, __________.

9. Aircraft fuel tanks have a low area called a __________ that is designed as a place for contaminants and water to settle.

10. Always route a fuel line below any __________ .

11. The most common electric motor operated fuel valves are the __________ valve and the __________ type valve.

12. A characteristic of solenoid operated fuel valves is that they open and close __________ .

13. The boost pump delivers fuel under positive pressure to the __________ .

14. Centrifugal fuel boost pumps used in aircraft with reciprocating engines ensure __________ pressure and are preventing __________ .

15. Reciprocating engine aircraft typically use a __________ engine driven fuel pump.

16. Fuel boost pumps on many large aircraft are used for several different fuel sub systems such as a __________, and __________ system.

17. Fuel strainers are designed to trap __________ pieces of debris and prevent their passage through the __________.

18. __________ filters are commonly used on turbine powered aircraft. This type of filter captures extremely fine particles in the range of __________ microns.

19. __________ are used in turbine powered aircraft to prevent the formation of ice in the fuel.

20. Modern aircraft use electric fuel quantity indicators which operate with __________ current.

21. Four basic classifications are used to describe aircraft fuel leaks. They are:
__________, __________, __________, __________

22. Heavy seeps are classified as an area of fuel from __________ to __________ in diameter that forms in 30 minutes.

23. When an integral fuel cell needs to be repaired the tank needs to __________ and tested with a __________ to be certain it can be entered safely.

24. Unstrained water can be detected by a __________ appearance to the fuel.

25. Two types of fueling processes are: __________ and __________.


1. A fuel jettison system is required on aircraft that have a higher take off weight than landing weight. TRUE/FALSE

2. Turbine fuel has a much lower flash point than AVGAS. TRUE/FALSE

3. Vapor lock can be caused by excessively hot fuel, low pressure, or excessive turbulence of the fuel traveling through the fuel system. TRUE/FALSE

4. Detonation could be recognized by a pinging or knocking sound and it causes a lower cylinder head temperature. TRUE/FALSE

5. AVGAS 100LL could be distinguished from other fuels by its blue color. TRUE/FALSE

6. Jet B fuel is the most common jet fuel in the United States and it allows engine restarts at high altitude. TRUE/FALSE

7. Low and mid wing single reciprocating engine aircraft use a gravity fuel system. TRUE/FALSE

8. large transport type aircraft typically use integral fuel tanks in each of their wing structures to store the fuel. TRUE/FALSE

9. A fuel transfer system allows fuel to be transferred from one fuel tank to another and a fuel cross feed system allows any engine to draw fuel from any tank. TRUE/FALSE

10. Aircraft equipped with integral fuel tanks do not have fuel vent systems instead they use fuel jettison systems to vent the fuel tanks. TRUE/FALSE

11. Motor and solenoid operated valves used in a fuel system use position enunciator lights to indicate valve position in addition to the switch position. TRUE/FALSE

12. The fuel boost pump delivers fuel under positive pressure to the fuel control. TRUE/FALSE

13. A centrifugal boost pump is a constant displacement pump. TRUE/FALSE

14. A sump is typically located in the highest part of the tank so that the water and contaminants can be drained before the flight. TRUE/FALSE

15. The most common type of fuel heaters for large transport category aircraft are air/fuel heaters and oil/fuel heaters. TRUE/FALSE

16. The flight crew uses information of the filter by‐pass indicating lights and fuel temperature gauge to know when to turn the fuel heaters on or fuel heaters can work automatically. TRUE/FALSE

17. The disadvantage of electronic fuel quantity systems is that they have many moving components. TRUE/FALSE

18. Many aircraft with capacitance type fuel indicating systems also use a mechanical indication system to cross check fuel quantity indications. TRUE/FALSE

19. Fuel flow meters in turbine aircraft measure the volume of the fuel consumed by the engine. TRUE/FALSE

20. A higher fuel flow indication should result in a higher exhaust gas temperature. TRUE/FALSE

21. When fuel leaks into a confined area the leak must be monitored every flight. TRUE/FALSE

22. Microorganisms appear as a visible slime that is dark brown, grey, red, or black in color. TRUE/FALSE

23. The best solution to stop microorganisms to grow in AVGAS is to keep water from accumulating in the fuel. TRUE/FALSE

24. The type of fuel to be used is placarded near the fill port on over‐the‐wing systems and at the fueling station on pressure refueled aircraft. TRUE/FALSE

25. Aircraft fuel boost pumps can be used on some aircraft to defuel the tanks or the pump of the fuel truck can be used to defuel the airplane. TRUE/FALSE

Knowledge Application Questions

1. What is the purpose of a fuel dump system incorporated in many transport category aircraft?

2. Name three types of fuel cells.
_______________________ _______________________ _______________________

3. What supports the weight of fuel in a bladder‐type fuel cell?

4. What is the purpose of a fuel temperature indicator in a turbine‐powered aircraft?

5. What is the purpose of a fuel crossfeed system in multiengine aircraft?

6. What 3 positions may be selected on a fuel tank selector valve?

7. What are drip gauges and sight gauges used for?

8. What type of fueling system is used on large transport category aircraft?

9. What are some advantages of single‐point pressure fueling?

10. What method may be used to check a fuel tank for leaks after a patch or weld has been performed?

11. What type of fuel system leak will not be visible by evidence of stains or wet spots?

12. Name four types of fuel quantity gauges that are common?
_____________________________ _____________________________
_____________________________ _____________________________

13. Why is an electronic‐type fuel quantity gauge more accurate than others?

14. What is the purpose of fuel tank internal baffles?

15. Why should you wait a period of time after fueling before checking fuel sumps?

16. What is the best way to stop microorganisms to grow in jet fuel?

Multiple Choices Questions

1. Fuel jettisoning is usually accomplished
a. by gravity flow into the outboard wing tanks and overboard through a common outlet in each wing.
b. through individual outlets for each tank.
c. through a common manifold and outlet in each wing.

2. The primary purpose of an aircraft's fuel jettison system is to quickly achieve a
a. lower landing weight.
b. reduced fire hazard.
c. balanced fuel load.

3. (1) The fuel jettison valve must be designed to allow flight personnel to close the valve during any part of the jettisoning operation.
(2) During the fuel jettisoning operation, the fuel must discharge clear of any part of the airplane.

Regarding the above statements,
a. neither No. 1 nor No. 2 is true.
b. both No. 1 and No. 2 are true.
c. only No. 2 is true.

4. Which of the following is employed to maintain lateral stability when jettisoning fuel?
a. Crossfeed system.
b. Two interconnected systems.
c. Two separate independent systems.

5. A fuel jettison system is required under certain conditions if the maximum takeoff weight exceeds the maximum landing weight. What regulations cover the requirements of fuel jettisoning?
a. Federal Aviation Regulation Part 43 and 91.
b. Federal Aviation Regulation Part 23, 25 and CAM 4b.
c. Federal Aviation Regulation Part 21, 43 and CAM 8.

6. Fuel is moved overboard in most fuel jettison systems by
a. gravity.
b. boost pumps.
c. gravity and engine driven fuel pumps.

7. Fuel jettisoning past the limits prescribed by Federal Aviation Regulations is usually prevented by
a. dump limit valves or a low-level circuit.
b. standpipes in the fuel tanks.
c. closely monitoring the fuel quantity and turning off the fuel dump switch(es).

8. Which procedure must be followed when defueling aircraft with sweptback wings?
a. Defuel all the tanks at one time.
b. Defuel the outboard wing tanks first.
c. Defuel the inboard wing tanks first.

9. (Refer to figure 1) What is the purpose of the pump crossfeed valve?
a. Balance the fuel in the tanks.
b. Allow operation of engines from one tank.
c. Allow operation of the left engine when the right fuel boost pump is inoperative.

Figure 1

10. Normal fuel cross-feed system operation in multiengine aircraft
a. reduces contamination and/or fire hazards during fueling or defueling operations.
b. provides a means to maintain a balanced fuel load condition.
c. calls for jettisoning of fuel overboard to correct lateral instability.

11. What is the primary purpose of the crossfeed system?
a. To provide automatic refueling of a tank to any desired level.
b. To allow the feeding of any engine from any tank.
c. To allow the feeding of fuel from one tank for defueling.

12. Fuel system components must be bonded and grounded in order to
a. retard galvanic corrosion.
b. drain off static charges.
c. prevent stray currents.

13. A typical large transport aircraft fuel manifold system allows how many of the following?
1. All tanks can be serviced through a single connection.
2. Any engine can be fed from any tank.
3. All engines can be fed from all tanks simultaneously.
4. A damaged tank can be isolated from the rest of the fuel system.

a. Three.
b. TWO.
c. Four.

14. The use of turbine fuels in aircraft has resulted in some problems not normally associated with aviation gasoline. One of these problems is
a. microbial contaminants.
b. increasing viscosity of fuel as fuel temperature lowers at altitude.
c. higher vapor pressure.

15. What is used in many aircraft to prevent bubbles in the fuel after it leaves the tank when atmospheric pressure is lower than fuel vapor pressure?
a. Air fuel separators.
b. Boost pumps.
c. Anti-foaming additives.

16. Which of the following precautions is most important during refueling operations?
a. Fuel to be used must be appropriately identified.
b. All electrical switches must be in OFF position.
c. All outside electrical sources must be disconnected from the aircraft.

17. Before fueling an aircraft by using the pressure fueling method, what important precaution should be observed?
a. The truck pump pressure must be adjusted for minimum filter pressure.
b. The aircraft's electrical system must be on to indicate quantity gauge readings.
c. The truck pump pressure must be correct for that refueling system.

18. What flight safety related advantage does a pressure fueling system provide?
a. Reduces the chances for fuel contamination.
b. Keeps the aircraft within weight and balance limitations.
c. Reduces the time required for fueling.

19. Aircraft pressure fueling systems instructional procedures are normally placarded on the
a. lower wing surface adjacent to the access door.
b. fuel control panel access door.
c. aircraft ground connection point.

20. Pressure fueling of aircraft is usually accomplished through
a. at least one single point connection.
b. individual fuel tank overwing and/or fuselage access points.
c. pressure connections on individual fuel tanks.

21. Which of the following may be used for the repair of fuel leaks on most integral fuel tanks?
a. Riveting and resealing.
b. Brazing and resealing.
c. Welding and resealing.

22. How is the outlet fuel pressure regulated on a submerged, single speed, centrifugal type fuel pump?
a. By the first check valve downstream from the pump.
b. By the pump's design and internal clearances.
c. By the engine driven pump's design and internal clearance.

23. What is one purpose of a fuel tank vent?
a. To decrease tank internal air pressure.
b. To decrease fuel vapor pressure.
c. To maintain atmospheric pressure.

24. When inspecting a removable rigid fuel tank for leaks, what procedure should be followed?
a. pressurize the tank with air and submerge in water to locate leaks.
b. pressurize the tank with air and brush with soapy water.
c. fill the tank with water and pressurize with air and brush with soapy water.

25. If it is necessary to enter an aircraft's fuel tank, which procedure should be avoided?
a. Conduct the defueling and tank purging operation in an air conditioned building.
b. Continue purging the tank during the entire work period.
c. Station an assistant outside the fuel tank access to perform rescue operations if required.

26. What is the recommended practice for cleaning a fuel tank before welding?
a. Steam clean the tank interior.
b. Flush the inside of the tank with clean water.
c. Purge the tank with air.

27. An aircraft's integral fuel tank is
a. a part of the aircraft structure.
b. usually located in the bottom of the fuselage.
c. a self sealing tank.

28. Which gas is used for purging an aircraft fuel tank?
a. Carbon monoxide.
b. Helium or argon.
c. Carbon dioxide.

29. Why is the main fuel strainer located at the lowest point in the fuel system?
a. It filters and traps all micro-organisms that may be present in the fuel system.
b. It provides a drain for residual fuel.
c. It traps any small amount of water that may be present in the fuel system.

30. The purpose of a diaphragm in a vane type fuel pump is to
a. compensate fuel pressures to altitude changes.
b. vary fuel pressure according to throttle setting.
c. equalize fuel pressure at all speeds.

31. When moving the mixture control on a normally operating engine into the idle cutoff position, engine RPM should
a. slightly increase before the engine starts to die.
b. remain the same until the cutoff is effected, then drop rapidly.
c. slightly decrease and then drop rapidly.

32. Entrained water in aviation turbine fuel is a hazard because of its susceptibility to freezing as it passes through the filters. What are common methods of preventing this hazard?
a. Micromesh fuel strainers and fuel heater.
b. Anti-icing fuel additives and fuel heater.
c. High-velocity fuel pumps and fuel heater.

33. Fuel leaks are usually classified as a stain, a seep, a heavy seep, or a running leak. As a general rule,
a. stains, seeps, and heavy seeps are not flight hazards.
b. all fuel leaks regardless of location or severity are considered a hazard to flight.
c. stains, seeps, and heavy seeps, (in addition to running leaks) are considered flight hazards when located in unvented areas of the aircraft.

34. The presence of fuel stains around a fuel nozzle would indicate
a. clogged fuel nozzle.
b. excessive airflow across the venturi.
c. too much fuel pressure.

35. What should be used to inert an integral fuel tank before attempting repairs?
a. CO2.
b. Steam.
c. Water.

36. What should be used to remove flux from an aluminum tank after welded repairs?
a. Soft brush and warm water.
b. 5 percent solution of nitric or sulfuric acid.
c. Mild solution of soap and warm water.

37. What method would be used to check for internal leakage of a fuel valve without removing the valve from the aircraft?
a. Apply regulated air pressure on the downstream side of the fuel pump and listen for air passing through the valve.
b. Place the valve in the OFF position, drain the strainer bowl, and with boost pump on, watch to see if fuel flows to the strainer bowl.
c. Remove fuel cap(s), turn boost pump(s) on, and watch for bubbling in the tanks.

38. Why are jet fuels more susceptible to water contamination than aviation gasoline?
a. Jet fuel is lighter than gasoline; therefore, water is more easily suspended.
b. Condensation is greater because of the higher volatility of jet fuels.
c. Jet fuel has a higher viscosity than gasoline.

39. When installing a rigid fuel line, 112 inch in diameter, at what intervals should the line be supported?
a. 12 inches.
b. 16 inches.
c. 24 inches.

40. The probe of a capacitance type fuel level gauge is essentially a
a. float actuated variable capacitor.
b. capacitor with fuel and air acting as one plate.
c. capacitor with fuel and air acting as a dielectric.

41. The capacitance type (electronic) fuel quantity indicator
a. has no moving parts in the tank.
b. has two tubes separated by a mica dielectric in the tank.
c. utilizes a float operated variable capacitor.

42. What type of remote reading fuel quantity indicating system has several probes installed in each fuel tank?
a. Direct reading.
b. Electromechanical.
c. Electronic.

43. Which aircraft fuel quantity indicating system incorporates a signal amplifier?
a. Electrical.
b. Sight glass.
c. Electronic.

44. A drip gauge may be used to measure
a. the amount of fuel in the tank.
b. system leakage with the system shut down.
c. fuel pump diaphragm leakage.

45. The electronic type fuel quantity indicating system consists of a bridge circuit,
a. an amplifier, an indicator, and a tank unit.
b. a tank, an amplifier, and an indicator.
c. a tank unit, a tank, and an amplifier.

46. A probe or a series of probes is used in what kind of fuel quantity indicating system?
a. Capacitor.
b. Synchro.
c. Selsyn.

47. Why is the capacitance fluid quantity indicating system more accurate in measuring fuel level than a mechanical type?
a. It measures by weight instead of volume.
b. Only one probe and one indicator are necessary for multiple tank configurations.
c. It measures in gallons and converts to pounds.

48. One advantage of electrical and electronic fuel quantity indicating systems is that
a. the indicators are calibrated in gallons; therefore, no conversion is necessary.
b. only one transmitter and one indicator are needed regardless of the number of tanks.
c. several fuel tank levels can be read on one indicator.

49. A fuel totalizer is a component which indicates the
a. total amount of fuel being consumed by all engines.
b. amount of fuel in any given tank.
c. amount of fuel in all tanks.

50. What is the dielectric (nonconducting material) in a capacitance type fuel quantity indicating system?
a. Outer shell of the capacitor.
b. Fuel in the tank
c. Fuel and air in the tank.

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