US Patent 6971241 Dual mode power unit having a combustor bypass system

A gas turbine engine integrates the functions of an auxiliary power unit (APU) with one or more functions of an ECS, and that is capable of operating in both an unfired mode and a fired mode. The gas turbine engine includes a combustor system that is configured to allow the gas turbine to quickly transition from the unfired mode to the fired mode, by bypassing a portion of the air flowing to the combustor system around the combustor.