Airplane Flying Handbook Practice Test

The main idea is to compare how much air bypasses the core to how much air goes through the core itself. The bypass ratio is the mass flow rate of air that goes around the core (through the bypass duct) divided by the mass flow rate through the gas generator portion, which is the engine core—the path that includes the compressor, the combustion chamber, and the turbine. The combustion chamber and turbine are parts of that core, so using the entire gas generator portion gives the correct denominator. The intake is just the air entering the engine and doesn’t define the core vs bypass split, so it isn’t used in the ratio.