Synchroscope Operation: Multi-Engine Propeller RPM Synchronization

022-01-08Pablo Asensio Martínez2026-03-271 min

In multi-engine propeller aircraft, unsynchronized engine speeds (RPM) generate uncomfortable "beat" noises and vibrations, leading to structural fatigue and passenger discomfort.

Purpose and Function

A Synchroscope allows pilots to manually synchronize the RPM of a "slave" engine to a "master" engine with high precision.

  • Mechanism: The instrument receives AC signals from the tacho-generators (alternators) of both engines. It compares the frequencies of these AC signals.
  • Indication:
    • If frequencies match, the engines are synchronized, and the indicator (a small rotating propeller or pointer) stops.
    • If the slave is faster, the pointer rotates in one direction.
    • If the slave is slower, it rotates in the opposite direction.
  • Operation: The pilot adjusts the throttle of the slave engine until rotation stops. Modern aircraft perform this synchronization automatically.
Written and reviewed by

Pablo Asensio · 2026-03-27

Aeronautical engineer. Passed the thirteen EASA ATPL(A) theoretical knowledge exams studying from these very notes. Writes and reviews each topic against the Part-FCL Learning Objectives.

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