Definition
In a turbofan engine, the annular passage that carries air around the core engine rather than through it. Air accelerated by the fan flows through the bypass duct and exits at the rear of the engine, producing a large portion of the engine's thrust without passing through the compressor, combustor, or turbine.
Plain English
A channel inside a jet engine that lets some of the incoming air go around the hot inner part of the engine instead of through it. That air still gets pushed out the back and helps create thrust.
Context Anchor
Seen in turbine engine descriptions, especially when learning how turbofan engines produce thrust.
Derivation
Bypass comes from 'by' (around) and 'pass' (to go through). The duct lets air go around the core engine rather than passing through it. Knowing this makes the function self-explanatory.
Why Pilots Care
Bypass ducts raise thrust, lower fuel burn, and reduce engine noise in modern jet aircraft.
Analogy
Think of a river splitting around an island. One part goes through the main channel, while another part goes around the island and rejoins the flow later. The bypass duct is the around-the-island path for engine air.
Intuition Check
Do not think of the bypass duct as an emergency detour or unused passage. In a turbofan engine, air flowing through the bypass duct is a normal and important part of how the engine makes thrust.
Example Sentence 1
Most of the thrust in a high-bypass turbofan comes from air moving through the bypass duct, not from the hot exhaust.
Example Sentence 2
Mechanics inspect the bypass duct for damage that could reduce engine efficiency.