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Fuel path during engine starting

Aviation Mechanic Powerplant (AMP) practice question 5 of 20 on Engine Fuel and Fuel Metering Systems. ACS element AM.III.I.K10 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONIn a basic aircraft fuel system, how does fuel from the boost pump reach the metering device during engine starting?

  1. AThrough the vapor vent return line
  2. BThrough the drain valve on the main line strainer
  3. CThrough a bypass in the engine-driven pump
Show the answer and explanation

Correct answer: C. Through a bypass in the engine-driven pump

  • A — incorrect The vapor vent line returns vapor and a small amount of fuel toward the supply tank; it does not carry the supply of fuel to the metering device.
  • B — incorrect The strainer drain valve is opened only to remove water and sediment; fuel passes through the strainer itself on the way to the engine-driven pump.
  • C — correct During starting the boost pump forces fuel through a bypass in the engine-driven pump to the metering device until the engine-driven pump turns fast enough to take over.

BACKGROUND

The basic parts of a fuel system include tanks, boost pumps, lines, selector valves, strainers, engine-driven pumps, and pressure gauges. From each tank a line leads to the selector valve, which is set from the flight deck to choose the tank supplying the engine. The boost pump forces fuel through the selector valve to the main line strainer, the filtering unit located in the lowest part of the system that removes water and dirt. During starting, the boost pump forces fuel through a bypass in the engine-driven pump to the metering device. Once the engine-driven pump is rotating at sufficient speed it takes over and delivers fuel to the metering device at the specified pressure.

STUDY TIP

Trace the system in order from tank to metering device and note which pump is doing the work at each stage. The bypass exists because the engine-driven pump cannot supply pressure until the engine is turning.

KEY POINTS

  • The boost pump moves fuel through the selector valve and main line strainer.
  • During starting, that fuel reaches the metering device through a bypass in the engine-driven pump.
  • Once up to speed, the engine-driven pump supplies fuel at the specified pressure.

SOURCES

  • amp-powerplant/ch02.txt "Basic Fuel System"
Practice the Aviation Mechanic Powerplant (AMP) test →Timed 100-question exam, by ACS area, or review your misses. Free.
MORE ON ENGINE FUEL AND FUEL METERING SYSTEMS

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-32B Aviation Maintenance Technician Handbook – Powerplant, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.