Definition
A turbine engine system that manages the gap (clearance) between the rotating turbine blade tips and the surrounding stationary case by directing cooling air onto the case to control its thermal expansion. By holding this gap as small as possible across different power settings, the engine loses less gas around the blade tips and runs more efficiently.
Plain English
A system that keeps the tiny gap between the spinning turbine blades and the engine casing as small as possible, by spraying cooling air on the outside of the case to shrink it just the right amount. A smaller gap means less hot gas leaks past the blades, so the engine burns less fuel for the same thrust.
Context Anchor
Seen in turbine engine maintenance, engine performance discussions, and troubleshooting of systems that manage engine temperatures and efficiency.
Derivation
Active means the system adjusts itself in real time, rather than relying on a fixed built-in clearance. Clearance is the small physical gap between two parts. Control means the system regulates that gap deliberately. Together: a system that actively regulates the blade-tip-to-case gap.
Why Pilots Care
It improves engine efficiency, reduces fuel burn, and prevents blade damage by keeping clearances tight without rubs.
Grounding Statement
As the engine heats up and metal parts grow, ACC helps keep the blade-to-case gap from becoming too large or too tight.
Intuition Check
Clearance here does not mean permission from air traffic control. It means the small physical gap between moving turbine blade tips and the fixed engine case.
Example Sentence 1
The active clearance control system reduces fuel consumption at cruise by holding turbine blade tip clearance to a minimum.
Example Sentence 2
Active clearance control activates during cruise to tighten blade tip gaps and improve fuel efficiency.