A hybrid electric propulsion system comprising: a gas turbine engine (20; 120) comprising a low speed spool and a high speed spool, the low speed spool comprising a low pressure compressor and a low pressure turbine, and the high speed spool comprising a high pressure compressor and a high pressure turbine; an electric motor (212A, 212B; 282) configured to augment rotational power of the high speed spool or the low speed spool; and a controller operable to: determine, based at least in part on an altitude and airspeed associated with the hybrid electric propulsion system, that an opposite engine power assist is prohibited; detect an in-flight windmill re-start condition of the gas turbine engine, wherein the in-flight windmill re-start condition of the gas turbine engine is based at least in part on the determination that opposite engine power assist is prohibited; and cause power to be supplied from a power source to the electric motor (212A, 212B; 282) in order to augment rotational power of the high speed or the low speed spool during the detected in-flight windmill re-start condition; wherein the controller and the electric motor (212A, 212B; 282) provide compressor stability to the high pressure compressor during the detected in-flight windmill re-start condition such that high pressure compressor bleed valves are not required. a gas turbine engine (20; 120) comprising a low speed spool and a high speed spool, the low speed spool comprising a low pressure compressor and a low pressure turbine, and the high speed spool comprising a high pressure compressor and a high pressure turbine; an electric motor (212A, 212B; 282) configured to augment rotational power of the high speed spool or the low speed spool; and a controller operable to: determine, based at least in part on an altitude and airspeed associated with the hybrid electric propulsion system, that an opposite engine power assist is prohibited; detect an in-flight windmill re-start condition of the gas turbine engine, wherein the in-flight windmill re-start condition of the gas turbine engine is based at least in part on the determination that opposite engine power assist is prohibited; and cause power to be supplied from a power source to the electric motor (212A, 212B; 282) in order to augment rotational power of the high speed or the low speed spool during the detected in-flight windmill re-start condition; determine, based at least in part on an altitude and airspeed associated with the hybrid electric propulsion system, that an opposite engine power assist is prohibited; detect an in-flight windmill re-start condition of the gas turbine engine, wherein the in-flight windmill re-start condition of the gas turbine engine is based at least in part on the determination that opposite engine power assist is prohibited; and cause power to be supplied from a power source to the electric motor (212A, 212B; 282) in order to augment rotational power of the high speed or the low speed spool during the detected in-flight windmill re-start condition; wherein the controller and the electric motor (212A, 212B; 282) provide compressor stability to the high pressure compressor during the detected in-flight windmill re-start condition such that high pressure compressor bleed valves are not required.