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Synchrophasing command signal destination

Aviation Mechanic Powerplant (AMP) practice question 8 of 10 on Propellers. ACS element AM.III.M.K8 · 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 an electronic propeller synchrophasing system, the corrected command signal is sent to an rpm trimming coil located on which unit?

  1. AThe governor of the slow engine
  2. BThe governor of the master engine
  3. CThe fuel control unit of each engine
Show the answer and explanation

Correct answer: A. The governor of the slow engine

  • A — correct The computed input signals are corrected into a command signal sent to an rpm trimming coil on the propeller governor of the slow engine, whose rpm is then adjusted to match the other propeller.
  • B — incorrect The master propeller sets the reference; it is the slower engine's governor that receives the trimming signal.
  • C — incorrect Synchrophasing acts through the propeller governors, not through the fuel control units, and it trims only one engine at a time.

BACKGROUND

Most multi-engine aircraft have propeller synchronization systems, which control and match engine rpm to reduce vibration and eliminate the beat produced by unsynchronized propellers. A synchrophasing system goes further and maintains a preset angular relationship between a designated master propeller and the slave propellers to reduce cabin noise. A typical synchrophasing system is electronic and is controlled by a two-position switch located forward of the throttle quadrant, which supplies direct current (DC) power to an electronic control box. Input signals representing propeller rpm come from a magnetic pickup on each propeller. The computed signals are corrected into a command signal sent to an rpm trimming coil on the governor of the slow engine, bringing its rpm up to that of the other propeller.

STUDY TIP

Trace the signal path once: magnetic pickups, control box, trimming coil on the slow engine's governor; that order answers most synchronization questions.

KEY POINTS

  • Synchrophasing holds a preset blade phase relationship between master and slave propellers.
  • Propeller rpm signals come from a magnetic pickup on each propeller.
  • The command signal trims the governor of the slow engine to match the other propeller.

SOURCES

  • sources/amp-powerplant/ch07.txt "Propeller synchronization" (synchrophasing system)
  • FAA-H-8083-32 ch07, Propeller Synchronization
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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.