Abstract: An apparatus and method is provided to start gas turbine engines at cold start. A gearbox is not mechanically coupled to any accessory or to the starter-generator. Rather, a controller is used to route power to a starter-generator to rotate the turbine mainshaft to start the gas turbine engine. The controller prevents power to an accessory drive motor, until the starter-generator creates a positive torque. When a positive torque is reached, excess power is routed to the accessory drive motor, typically a brushless direct current motor.

Abstract: 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.