Q&A | Engine Fuel and Fuel Metering Systems

Fill in the Blanks

1. The partial or complete interruption of fuel flow due to the presence of vapor in fuel lines is called
__________.

2. The primary purpose of a boost pump is to prevent main fuel pump __________ and system __________.

3. The main fuel pumps used with turbine engines are generally the __________ type.

4. A __________ (what type) boost element may be built into the engine driven fuel pump.

5. The fluid used in a water injection system is a mixture of water and __________.

6. Water injection in a turbine engine is a means of __________ augmentation.

7. The chemically perfect mixture of air and fuel (stoichiometric mixture) consists of __________ pounds of air for each pound of fuel.

8. Carburetors in which the air passes upward through the unit are called __________ carburetors.

9. The throttle valve of a float-type carburetor is located between the __________ and the engine.

10. The fuel level in the float chamber is usually kept about __________ inch below the opening in the main discharge nozzle.

11. The __________ system determines the ratio of fuel to air in the mixture.

12. The __________ system is used to shut off the fuel and stop the engine.

13. When a carburetor equipped with a back suction mixture control is in the lean position, the pressure in the float chamber is the same as the pressure at the __________.

14. The power enrichment system is sometimes called an __________ system.

15. Carburetor controls should be rigged so they have an equal amount of __________ at both ends of their travel.

16. A water injection system used on reciprocating engines may also be referred to as __________ injection.

17. Vapor is removed from the fuel in a Teledyne Continental Motors fuel injection system in the __________ (what unit).

18. The orifice in a Teledyne Continental Motors fuel injection pump used with a turbocharged engine is automatically adjusted by an evacuated __________.

19. The orifice size in a Teledyne Continental Motors fuel injection pump is varied by the amount of upper deck pressure. This pressure is actually the __________ pressure.

20. The manual mixture control in a Teledyne Continental Motors fuel injection system is a form of __________ valve.

True or False

1. Fuel which vaporizes too readily can cause vapor lock. (True/False)

2. Two levels of filtration are normally required in turbine engine fuel systems. (True/False)

3. As the velocity of air increases in the throat of a venturi, the pressure of the air will increase. (True/False)

4. A reciprocating engine will develop maximum power with a mixture of approximately 12:1. (True/False)

5. Carburetors tend to run richer at ground level. (True/False)

6. A float-type carburetor discharges the fuel downstream of the throttle valve. (True/False)

7. Air bled into the main metering system decreases fuel density and destroys surface tension. (True/False)

8. The acceleration system supplies extra fuel when the throttle is opened quickly. (True/False)

9. A pressure carburetor discharges fuel upstream of the throttle valve. (True/False)

10. The mixture control in a pressure carburetor varies the fuel/air ratio by controlling the air metering force. (True/False)

11. Direct injection fuel injection systems meter the fuel and deliver it to the intake port of each cylinder. (True/False)

12. RSA fuel injector nozzles are not interchangeable between engines and between cylinders. (True/False)

13. Lengthening the connecting rod between the throttle fuel valve and the throttle air valve of an RSA injection system richens the idling fuel/air mixture. (True/False)

14. The adjustable orifice in a Teledyne Continental Motors fuel injection pump adjusts the low unmetered fuel pressure. (True/False)

15. The relief valve in the Teledyne Continental Motors fuel injection pump adjusts the low unmetered fuel pressure. (True/False)

Knowledge Application Questions

1. What is the purpose of the bypass valve in an engine driven fuel pump?

2. On which side of the firewall is the engine fuel shutoff valve located?

3. What are three purposes for the boost pumps in an aircraft fuel system?

4. What kind of boost pump is used in most aircraft fuel systems?

5. Where does an engine-driven fuel pump direct the excess fuel from its pressure relief valve?

6. What causes a vapor lock in an aircraft fuel system?

7. What is done in most aircraft fuel systems to prevent vapor lock?

8. What is meant by a compensated relief valve in an engine-driven fuel pump?

9. What is the purpose of the pressurizing and dump valve in the fuel system for a turbine engine?

10. What should be done to an aircraft reciprocating engine if it has been operated on turbine engine fuel?

11. What are the two basic types of turbine engine fuel?

12. Why do some turbine engine fuel systems incorporate a fuel heater?

13. What are two reasons Prist is used in turbine engine fuel?

14. Why do some aircraft fuel filters have a built-in relief valve?

15. Where does the fuel metering system of a turbine engine discharge its fuel?

Multiple Choice Questions

1. During what period does the fuel pump bypass valve open and remain open?
a. When the fuel pump pressure is greater than the demand of the engine.
b. When the boost pump pressure is greater than fuel pump pressure.
c. When the fuel pump output is greater than the demand of the carburetor.

2. Which of the following statements concerning a centrifugal-type fuel boost pump located in a fuel supply tank is NOT true?
a. Air and fuel vapors do not pass through a centrifugal-type pump.
b. Fuel can be drawn through the impeller section of the pump when it is not in operation.
c. The centrifugal-type pump is classified as a positive displacement pump.

3. Where is the engine fuel shutoff valve usually located?
a. Aft of the firewall.
b. Adjacent to the fuel pump.
c. Downstream of the engine-driven fuel pump.

4. Boost pumps in a fuel system
a. operate during takeoff only.
b. are primarily used for fuel transfer.
c. provide a positive flow of fuel to the engine pump.

5. (Refer to Figure 1.) What is the purpose of the fuel transfer ejectors?
a. To supply fuel under pressure to the engine-driven pump.
b. To assist in the transfer of fuel from the main tank to the boost pump sump.
To transfer fuel from the boost pump sump to the wing tank.

Aircraft engine fuel system starter generator circuit

Figure 1. Starter-Generator circuit

6. What is the purpose of an engine-driven fuel pump bypass valve?
a. To divert the excess fuel back to the main tank.
b. To prevent a damaged or inoperative pump from blocking the fuel flow of another pump in series with it.
c. To divert the excess fuel from the pressure side of the pump to the inlet side of the pump.

7. Most large aircraft reciprocating engines are equipped with which of the following types of engine-driven fuel pumps?
a. Rotary-vane-type fuel pump.
b. Centrifugal-type fuel pump.
c. Gear-type fuel pump.

8. When an electric primer is used, fuel pressure is built up by the
a. internal pump in the primer solenoid.
b. suction at the main discharge nozzle.
c. booster pump.

9. The fuel pump relief valve directs excess fuel to the
a. fuel tank return line.
b. inlet side of the fuel pump.
c. inlet side of the fuel strainer.

10. Which type of pump is commonly used as a fuel pump on reciprocating engines?
a. Gear.
b. Impeller.
c. Vane.

11. The purpose of the diaphragm in most vane-type fuel pumps is to
a. maintain fuel pressure below atmospheric pressure.
b. equalize fuel pressure at all speeds.
c. compensate fuel pressures to altitude changes.

12. The primary condition(s) that allow(s) microorganisms to grow in the fuel in aircraft fuel tanks is (are)
a. warm temperatures.
b. the presence of water.
c. the presence of dirt or other particulate contaminants.

13. It is desirable that fuel lines have a gentle slope upward or downward and not have sharp curves or sharp rises and/or falls in order to
a. prevent vapor lock.
b. prevent stagnation or “pooling” of fuel in the fuel lines.
c. minimize the generation of static electricity by decreasing fluid friction in the lines.

14. The fuel systems of aircraft certificated in the standard classification must include which of the following?
a. An engine-driven fuel pump and at least one auxiliary pump per engine.
b. A positive means of shutting off the fuel to all engines.
c. A reserve supply of fuel, available to the engine only after selection by the flight crew, sufficient to operate the engines at least 30 minutes at METO power.

15. Where is the main fuel strainer located in the aircraft fuel system?
a. At the highest point in the fuel system.
b. At the lowest point in the fuel system.
c. At the inlet chamber of the carburetor.

16. Where physical separation of the fuel lines from electrical wiring or conduit is impracticable, locate the fuel line
a. below the wiring and clamp the line securely to the airframe structure.
b. above the wiring and clamp the line securely to the airframe structure.
c. inboard of the wiring and clamp both securely to the airframe structure.

17. What is a characteristic of a centrifugal-type fuel boost pump?
a. It separates air and vapor from the fuel.
b. It has positive displacement.
c. It requires a relief valve.

18. The Federal Aviation Regulations require the fuel flow rate for gravity systems (main and reserve) to be
a. 125 percent of the takeoff fuel consumption of the engine.
b. 125 percent of the maximum, except takeoff, fuel consumption of the engine.
c. 150 percent of the takeoff fuel consumption of the engine.

19. Fuel boost pumps are operated
a. to provide a positive flow of fuel to the engine.
b. during takeoff only.
c. primarily for fuel transfer to another tank.

20. A pilot reports that the fuel pressure fluctuates and exceeds the upper limits whenever the throttle is advanced. The most likely cause of the trouble is
a. a ruptured fuel pump relief-valve diaphragm.
b. a sticking fuel pump relief valve.
c. an air leak at the fuel pump relief-valve body.

21. A fuel strainer or filter must be located between the
a. boost pump and tank outlet.
b. tank outlet and the fuel metering device.
c. boost pump and engine-driven fuel pump.

22. Fuel pump relief valves designed to compensate for atmospheric pressure variations are known as
a. compensated-flow valves.
b. pressurized-relief valves.
c. balanced-type relief valves.

23. Fuel lines are kept away from sources of heat, and sharp bends and steep rises are avoided to reduce the possibility of
a. liquid lock.
b. vapor lock.
c. positive lock.

24. Fuel crossfeed systems are used in aircraft to
a. purge the fuel tanks.
b. jettison fuel in an emergency.
c. maintain aircraft stability.

25. If an engine equipped with a float-type carburetor backfires or misses when the throttle is advanced, a likely cause is that the
a. float level is too high.
b. main air bleed is clogged.
c. accelerating pump is not operating properly.

26. A fuel pressure relief valve is required on
a. engine-driven diaphragm-type fuel pumps.
b. engine-driven vane-type fuel pumps.
c. centrifugal fuel boost pumps.

27. A rotary-vane pump is best described as a
a. positive-displacement pump.
b. variable-displacement pump.
c. boost pump.

28. Fuel pressure produced by the engine-driven fuel pump is adjusted by the
a. bypass valve adjusting screw.
b. relief valve adjusting screw.
c. engine-driven fuel pump adjusting screw.

29. Kerosene is used as turbine engine fuel because
a. kerosene has very high volatility which aids in ignition and lubrication.
b. kerosene has more heat energy per gallon and lubricates fuel system components.
c. kerosene does not contain any water.

30. What are the principal advantages of the duplex fuel nozzle used in many turbine engines?
a. Restricts the amount of fuel flow to a level where more efficient and complete burning of the fuel is achieved.
b. Provides better atomization and uniform flow pattern.
c. Allows a wider range of fuels and filters to be used.

31. It is necessary to control acceleration and deceleration rates in turbine engines in order to
a. prevent blowout or die-out.
b. prevent overtemperature.
c. prevent friction between turbine wheels and the case due to expansion and contraction.

32. Which of the following turbine fuel filters has the greatest filtering action of any present-day filter type?
a. Micron filter.
b. Plain screen mesh filter.
c. Wafer screen filter.

33. What is the purpose of the flow divider in a turbine engine duplex fuel nozzle?
a. Allows an alternate flow of fuel if the primary flow clogs or is restricted.
b. Creates the primary and secondary fuel supplies.
c. Provides a flow path for bleed air which aids in the atomization of fuel.

34. What causes the fuel divider valve to open in a turbine engine duplex fuel nozzle?
a. Fuel pressure.
b. Bleed air after the engine reaches idle RPM.
c. An electrically operated solenoid.

35. How often should float carburetors be overhauled?
a. At engine overhaul.
b. Annually.
c. At engine change.

36. What is the final authority for the details of carburetor overhaul?
a. The local FAA safety inspector.
b. The Type Certificate Data Sheets for the engine.
c. The manufacturer’s recommendations.

37. Excessively rich or lean idle mixtures result in
a. too rapid completion of combustion.
b. incomplete combustion.
c. incomplete cylinder scavenging.

38. Which statement is true regarding proper throttle rigging of an airplane?
a. The throttle stop on the carburetor must be contacted before the stop in the cockpit.
b. The stop in the cockpit must be contacted before the stop on the carburetor.
c. The throttle control is properly adjusted when neither stop makes contact.

39. What precaution should be taken when putting thread lubricant on a tapered pipe plug in a carburetor float bowl?
a. Put the thread lubricant only on the first thread.
b. Do not use thread lubricant on any carburetor fitting.
c. Engage the first thread of the plug, then put a small amount of lubricant on the second thread and screw the plug in.

40. Maximum power is normally considered to be developed in a reciprocating engine with a fuel/air mixture ratio of approximately
a. 8:1.
b. 12:1.
c. 15:1.

41. What factor is not used in the operation of an aircraft gas turbine engine fuel control unit?
a. Compressor inlet air temperature.
b. Mixture control position.
c. Power lever position.

42. In order to stabilize cams, springs, and linkages within the fuel control, manufacturers generally recommend that all final turbine engine trim adjustments be made in the
a. increase direction.
b. decrease direction.
c. decrease direction after over-adjustment.

43. When trimming a turbine engine, the fuel control is adjusted to
a. produce as much power as the engine is capable of producing.
b. set idle RPM and maximum speed or EPR.
c. allow the engine to produce maximum RPM without regard to power output.

44. An electronic engine control (EEC) is a system that receives engine operating information and
a. adjusts a standard hydromechanical fuel control unit to obtain the most effective engine operation.
b. develops the commands to various actuators to control engine parameters.
c. controls engine operation according to ambient temperature, pressure, and humidity.

45. A full-authority electronic engine control (EEC) is a system that receives all the necessary data for engine operation and
a. adjusts a standard hydromechanical fuel control unit to obtain the most effective engine operation.
b. develops the commands to various actuators to control engine parameters.
c. controls engine operation according to ambient temperature, pressure, and humidity.

46. In a supervisory EEC system, any fault in the EEC that adversely affects engine operation
a. causes redundant or backup units to take over and continue normal operation.
b. usually degrades performance to the extent that continued operation can cause damage to the engine.
c. causes an immediate reversion to control by the hydromechanical fuel control unit.

47. The active clearance control (ACC) portion of an EEC system aids turbine engine efficiency by
a. adjusting stator vane position according to operating conditions and power requirements.
b. ensuring turbine blade to engine case clearances are kept to a minimum by controlling case temperatures.
c. automatically adjusting engine speed to maintain a desired EPR.

48. What should be checked/changed to ensure the validity of a turbine engine performance check if an alternate fuel is to be used?
a. Fuel specific gravity setting.
b. Maximum RPM adjustment.
c. EPR gauge calibration.

49. Prior to performing engine trimming, you should
a. call the control tower to obtain current sea level barometric pressure and temperature.
b. observe the reading on the aircraft outside air temperature (OAT) gauge.
c. obtain a true temperature reading comparable to that of the air that enters the engine.

50. An aircraft should be facing into the wind when trimming an engine. However, if the velocity of the wind blowing into the intake is excessive, it is likely to cause a
a. false low exhaust gas temperature reading.
b. trim setting resulting in engine overspeed.
c. false high compression and turbine discharge pressure, and a subsequent low trim.

Aircraft engine fuel system question paper for FAA A&P exam

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ANSWERS

Fill in the Blanks
1. vapor lock
2. cavitation, vapor lock
3. spur gear
4. centrifugal
5. alcohol
6. thrust
7. 15
8. updraft
9. venturi
10. 1/8

True or False
1. true
2. true
3. false
4. true
5. false
6. false
7. true

Knowledge Application
1. The bypass valve allows fuel to flow around the engine-driven pump for starting and for emergency operation if the engine-driven pump should fail.
2. The shutoff valve must be on the side of the firewall away from the engine.
3. To provide fuel pressure for starting the engine, to pressurize the fuel lines to prevent vapor lock, and to transfer fuel from one tank to another.
4. Electrically operated centrifugal pumps.
5. Back to the inlet side of the pump.
6. The fuel becomes hot enough that it boils. Vapors are released from the liquid fuel, and these vapors block the fuel lines so the liquid fuel cannot flow to the engine.
7. Boost pumps in the fuel tank pressurize the fuel in the lines and force the fuel into the fuel metering system.

Multiple Choice
1. b
When an aircraft's boost pump pressure exceeds that of the primary fuel pressure pump, a bypass valve in the pressure pump opens and allows fuel to flow directly to the engine. This occurs during start, when the pressure pump is not operating, and any time the engine driven fuel pump becomes clogged or fails.

2. c
A positive displacement pump provides a fixed quantity of fuel per pump revolution. With a centrifugal-type fuel boost pump, once the pressure builds to a predetermined pressure, fuel bypasses the impeller and remains in the fuel tank. Therefore, the pump does not continually displace fuel and is not a positive displacement pump.

3. a
According to the 14 CFR 23.995, the engine fuel shutoff valve may not be located on the engine side of the firewall.

4. c
The primary purpose of a fuel boost pump is to provide a positive flow of fuel to the engine driven pump.

5. b
A fuel transfer ejector helps transfer fuel from the main tank to the boost pump sump by creating a low pressure area at the fuel pick-up point. By pumping fuel past the venturi in the injector, a low pressure area is created that drains fuel into the line that feeds the boost pump sump.

6. b
When an aircraft's boost pump pressure is greater than that of the main pressure pump, a bypass valve in the pressure pump opens and allows fuel to flow directly to the engine. This prevents a damaged or inoperative pump from blocking fuel flow to the engine.

7. a
The purpose of the engine-driven fuel pump is to deliver a continuous supply of fuel at the proper pressure at all times during engine operation. Therefore, a positive displacement pump must be used. One type of positive displacement pump that is widely used is the rotary-vane-type fuel pump.

8. c
One of the many purposes of a boost pump is to supply fuel under pressure for priming prior to starting an engine.

9. b
Engine-driven fuel pumps typically discharge more fuel than an engine requires. Therefore, fuel systems must incorporate a relief valve to prevent the build up of excessive fuel pressures at the carburetor. A typical fuel pump relief valve is spring-loaded and, when opened, allows excess fuel to flow back to the inlet side of the fuel pump.

10. c
The purpose of the engine-driven fuel pump is to deliver a continuous supply of fuel at the proper pressure at all times during engine operation. Therefore, a positive displacement pump must be used. One type of positive displacement pump that is widely used is the rotary-vane-type fuel.

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