Definition
A device on a turbine engine that measures the rotational speed of the engine's core (the high-pressure compressor and turbine assembly, often called N2 on a two-spool engine or N3 on a three-spool engine) and sends that information to the engine indicating system or electronic engine control.
Plain English
A sensor that watches how fast the inner, high-pressure section of a jet engine is spinning and reports that speed back to the cockpit gauges or the engine's computer.
Context Anchor
Seen in turbine engine maintenance, engine-start troubleshooting, and engine speed indication discussions.
Derivation
The 'core' of a turbine engine is the inner, high-pressure section that drives the engine's combustion process, as distinct from the outer fan or low-pressure spool. 'Sensor' comes from the Latin sentire, meaning 'to feel or perceive.' So a core speed sensor literally 'feels' how fast the engine's core is turning.
Why Pilots Care
Monitors engine health and performance to detect issues such as stalls or failures.
Intuition Check
Do not read “speed” here as aircraft speed. A core speed sensor measures how fast part of the engine is turning, not how fast the airplane is moving.
Example Sentence 1
After engine start, the pilot cross-checked the N2 reading from the core speed sensor to confirm the engine had stabilised at idle.
Example Sentence 2
A drop in the core speed sensor value alerted the crew to a possible compressor problem.