Definition
A seal that prevents the leakage of air between two components, typically between stages of a turbine engine compressor or turbine, or between rotating and stationary parts where pressurized air must be contained or directed.
Plain English
A barrier inside an engine or system that stops air from leaking where it shouldn't go, keeping pressurized air on the correct side of a moving or fixed part.
Context Anchor
Seen during aircraft maintenance or preflight inspection around doors, windows, engine baffles, ducts, and other places where airflow or pressure must be controlled.
Derivation
Seal comes from an old word for something used to close or secure. In aircraft use, a seal is a part that closes a gap; an air seal specifically closes a gap against air leakage.
Why Pilots Care
A worn or failed air seal allows pressurized air to leak across stages, which reduces engine efficiency, increases fuel burn, and can cause performance loss or hot section damage.
Analogy
An air seal works like the weatherstripping around a house door: it closes the small gap so air does not leak through.
Intuition Check
Do not think of an air seal as a stamped approval or paperwork seal. Here, a seal is a physical part that blocks or reduces air leakage.
Example Sentence 1
The mechanic inspected the air seal between the compressor stages for signs of wear during the engine overhaul.
Example Sentence 2
Leaking air seals in the turbine section reduced overall engine efficiency during the test run.