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Governor underspeed condition

Aviation Mechanic Powerplant (AMP) practice question 3 of 10 on Propellers. ACS element AM.III.M.K3 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONA constant-speed propeller system is running below the rpm the pilot has selected. In this underspeed condition, what does the governor do?

  1. ALocks the blades at their current angle
  2. BDrains oil from the propeller piston to increase pitch
  3. CMeters oil to decrease blade pitch
Show the answer and explanation

Correct answer: C. Meters oil to decrease blade pitch

  • A — incorrect The governor corrects rpm by metering oil to and from the propeller piston; holding the blades at a fixed angle would leave the engine below the selected rpm.
  • B — incorrect Releasing oil so the blade flyweights move the blades toward high pitch is the governor's response to an overspeed condition, which slows the engine down.
  • C — correct With too little centrifugal force on the flyweights, they tilt inward and the speeder spring forces the pilot valve down, metering oil flow to decrease propeller pitch and raise engine rpm.

BACKGROUND

A propeller governor is an engine rpm-sensing device and a high-pressure oil pump that holds engine speed constant by changing blade angle. Rotating flyweights in the governor work against a speeder spring whose tension is set by the flight deck propeller control. When the flyweights spin faster than the spring tension allows, they fly outward, which is an overspeed condition, and the pilot valve releases oil so the blades move toward high pitch and the engine slows. When engine speed falls below the selected rpm, the flyweights tilt inward and the pilot valve is forced down, metering oil that decreases pitch and lets rpm rise. When the two forces balance, the system is on speed.

STUDY TIP

Remember that in a typical system governor oil pressure drives the blades toward low pitch, so an underspeed condition calls for oil to the propeller and an overspeed condition calls for oil to be released.

KEY POINTS

  • Underspeed: flyweights tilt inward, pilot valve moves down, pitch decreases and rpm rises.
  • Overspeed: flyweights fly outward, oil is released, pitch increases and rpm falls.
  • On speed exists when flyweight force and speeder spring tension are balanced.

SOURCES

  • sources/amp-powerplant/ch07.txt "Underspeed Condition"
  • sources/amp-powerplant/ch07.txt "Governor Mechanism"
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MORE ON PROPELLERS

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.