Definition
An instrument used on multi-engine aircraft that shows the difference in rotational speed (RPM) between two engines. It indicates whether one engine is turning faster or slower than the other, and by how much, allowing the pilot to match engine speeds precisely.
Plain English
A cockpit gauge that tells the pilot whether two engines are spinning at exactly the same speed, and if not, which one is faster.
Context Anchor
Seen in multiengine airplanes when the pilot is setting engine power and matching propeller speeds.
Derivation
From Greek 'syn' (together) and 'chronos' (time), combined with 'scope' (an instrument for viewing). Literally 'an instrument for viewing things in time together' — fitting, since it shows whether two engines are running in time with each other.
Why Pilots Care
Proper synchronization reduces vibration, improves passenger comfort, and prevents uneven wear on engines and propellers.
Intuition Check
A synchroscope does not usually make the engines match by itself. It shows the difference so the pilot, or a separate propeller synchronizing system, can correct it.
Example Sentence 1
After levelling off in cruise, the pilot adjusted the right propeller control until the synchroscope stopped rotating, indicating both engines were turning at the same RPM.
Example Sentence 2
In cruise flight the crew monitored the synchroscope to keep both engines matched for smooth operation.