Questions and Answers - 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. Why are integral fuel tanks used in many large aircraft?
a. To reduce fire hazards
b. To facilitate servicing
c. To reduce weight

2. Regarding the below statements:
(1) A fuel pressure relief valve is required on an aircraft positive displacement fuel pump.
(2) A fuel pressure relief valve is required on an aircraft centrifugal fuel boost pump.

a. only No. 1 is true
b. only No. 2 is true
c. both No. 1 and No. 2 are true

3. Regarding the below statements:
(1) A fuel heater can use engine bleed air as a source of heat.
(2) A fuel heater can use engine lubricating oil as a source of heat.

a. only No. 1 is true
b. both No. 1 and No. 2 are true
c. neither No. 1 nor No. 2 is true

4. Regarding the below statements:
(1) The function of a fuel heater is to protect the engine fuel system from ice formation.
(2) An aircraft fuel heater cannot be used to thaw ice in the fuel screen.

a. only No. 1 is true.
b. only No. 2 is true
c. both No. 1 and No. 2 are true

5. Aircraft defueling should be accomplished:
a. with the aircraft's communication equipment on and in contact with the tower in case of fire. 
b. in a hangar where activities can be controlled.
c. in the open air for good ventilation.

6. What method is used on turbine powered aircraft to determine when the condition of the fuel is approaching the danger of forming ice crystals?
a. Fuel pressure warning
b. Fuel pressure gauge
c. Fuel temperature indicator

7. In an electronic type fuel quantity indicating system, the tank sensing unit is a:
a. capacitor
b. variable resistor
c. variable inductor

8. To prevent vapor lock in fuel lines at high altitude, some aircraft are equipped with:
a. vapor separators
b. direct injection type carburetors
c. booster pumps

9. If a bladder type fuel tank is to be left empty for an extended period of time, the inside of the tank should be coated with a film of:
a. engine oil
b. linseed oil
c. ethylene glycol

10. Which of the following could result if microbial growth exists in a jet fuel tank and is not corrected?
1. Interference with fuel flow
2. Interference with fuel quantity indicators
3. Engine seizure
4. Electrolytic corrosive action in a metal tank
5. Lower grade rating of the fuel 6. Electrolytic corrosive action in a rubber tank

a. 1, 2, 4
b. 2, 3, 5
c. 1, 5, 6

11. Regarding the below statements:
(1) If aviation gasoline vaporizes too readily, fuel lines may become filled with vapor and cause increased fuel flow.
(2) A measure of a gasoline's tendency to vapor lock is obtained from the Reid vapor pressure test.

a. only No. 2 is true
b. both No. 1 and No. 2 are true
c. neither No. 1 nor No. 2 is true

12. Regarding the below statements:
(1) On a large aircraft pressure refueling system, a pressure refueling receptacle and control panel will permit one person to fuel or defuel any or all fuel tanks of an aircraft.
(2) Because of the fuel tank area, there are more advantages to a pressure fueling system in light aircraft.

a. only No. 1 is true
b. only No. 2 is true
c. both No. 1 and No. 2 are true

13. A fuel temperature indicator is located in the fuel tanks on some turbine powered airplanes to tell when the fuel may be:
a. getting cold enough to form hard ice
b. in danger of forming ice crystals
c. about to form rime ice

14. What type of fuel booster pump requires a pressure relief valve?
a. Concentric
b. Vane
c. Centrifugal

15. According to Part 23, what minimum required markings must be placed at or near each appropriate fuel filler cover for reciprocating engine‐powered airplanes?
a. The word 'Avgas' and the minimum fuel grade
b. The word 'Fuel' and usable fuel capacity
c. The word 'Avgas' and the total fuel capacity

16. Why is it necessary to vent all aircraft fuel tanks?
a. To ensure a positive head pressure for a submerged boost pump
b. To exhaust fuel vapors
c. To limit pressure differential between the tank and atmosphere

16 Flapper valves are used in fuel tanks to:
a. reduce pressure
b. prevent a negative pressure
c. act as check valves

17. What minimum required markings must be placed on or near each appropriate fuel filler cover on utility category aircraft?
a. The word 'Avgas' and the minimum fuel grade, and the total fuel tank capacity
b. The word 'Avgas' and the minimum fuel grade for the engines, and the usable fuel tank capacity
c. The word 'Avgas' and the minimum fuel grade

18. The use of turbine fuels in aircraft has resulted in some problems not normally associated with aviation gasoline. One of these problems is:

a. increasing viscosity of fuel as fuel temperature lowers at altitude
b. higher vapor pressure
c. microbial contaminants

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

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

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

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

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

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

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

26. A capacitance type fuel quantity indicating system measures fuel in:
a. pounds
b. pounds per hour
c. gallons

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

28. 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

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

30. What method would check for internal leakage of a fuel valve without removing the valve from the aircraft?
a. 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
b. Remove fuel cap(s), turn boost pump(s) on, and watch for bubbling in the tanks
c. Apply air pressure on the downstream side of the fuel pump and listen for air passing through the valve

Basic Fuel System Requirements
Fuel Tanks
Types of Aviation Fuel
Aircraft Fuel Systems
Fuel System Repair
Aircraft Fuel System Servicing
Fueling and Defueling Procedures
Fuel System Components
Types of Fuel Tanks
Types of Fuel Valves
Types of Fuel Pumps
Filters and Strainers
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