Which term describes the air in a turbofan that bypasses the engine core?

• A. Bypass air
• B. Core air
• C. Induction air
• D. Vent air

Answer: (A)

Bypass air is the air that flows through the bypass duct around the engine core in a turbofan. It does not enter the combustion chamber; instead, the fan moves a large volume of air around the core and exits the nozzle to produce thrust. This is why high-bypass turbofans rely on bypass air for most of their propulsion—it's cooler, quieter, and still provides substantial thrust because of the mass of air being accelerated. Core air, by contrast, is the air that goes into the engine core to be compressed, burned, and then expelled as hot exhaust. Induction air is a general term for air entering the engine, not specifically the bypass stream, and vent air isn’t a standard term used for turbofan airflow.