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Share of turbofan thrust available for reversing

Aviation Mechanic Powerplant (AMP) practice question 7 of 8 on Engine Exhaust and Reverser Systems. ACS element AM.III.L.K4 · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONA turbofan engine develops 24,000 pounds of total thrust. Based on the share of engine thrust that makes the fan the best source of reverse thrust, about how much thrust does the fan produce?

  1. AAbout 19,200 pounds
  2. BAbout 4,800 pounds
  3. CApproximately 12,000 pounds
Show the answer and explanation

Correct answer: A. About 19,200 pounds

  • A — correct The fan can produce approximately 80 percent of the engine's thrust, which is why it is the best source of reverse thrust; 80 percent of 24,000 pounds is 19,200 pounds.
  • B — incorrect This is 20 percent of the total and reverses the split; the core, not the fan, accounts for the smaller remaining share of thrust.
  • C — incorrect An even split between fan and core is not what the handbook describes; if the fan produced only half the thrust it would not be singled out as the best source of reverse thrust.

BACKGROUND

As aircraft gross weights and landing airspeeds increased, brakes alone could no longer be relied upon to stop an aircraft within a reasonable distance immediately after touchdown. Thrust reverser systems fall into two categories: mechanical-blockage and aerodynamic-blockage. A modern aerodynamic-blockage system, used mainly with unducted turbofan engines, consists of a translating cowl, blocker doors, and cascade vanes that redirect the fan airflow forward to slow the aircraft. Only fan air is used in this arrangement. Because the fan can produce approximately 80 percent of the engine's thrust, it is the best source for reverse thrust.

STUDY TIP

Anchor the 80 percent figure to the reason it matters: the fan is where the thrust is, so the fan is where reverse thrust is taken from. Then the arithmetic is a single multiplication.

KEY POINTS

  • The fan can produce approximately 80 percent of a turbofan engine's thrust.
  • That is why an aerodynamic-blockage reverser redirects only fan air to slow the aircraft.
  • Aerodynamic-blockage systems use a translating cowl, blocker doors, and cascade vanes.

SOURCES

  • sources/amp-powerplant/ch03.txt "Thrust Reversers"
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MORE ON ENGINE EXHAUST AND REVERSER 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.