Abstract: An hybrid aircraft power plant, has: a gas turbine engine having a high-pressure spool including a high-pressure compressor, a high-pressure turbine, and a high-pressure shaft drivingly engaging the high-pressure turbine to the high-pressure compressor, a low-pressure spool including a low-pressure compressor, a low-pressure turbine, and a low-pressure shaft drivingly engaging the low-pressure turbine to the low-pressure compressor; an electric motor drivingly engaged to the low-pressure shaft; and a torque-transmitting device operatively connected to the HP-shaft and having an engaged configuration in which the torque-transmitting device drivingly engages the electric motor to the high-pressure shaft and a disengaged configuration in which the torque-transmitting device disconnects the electric motor from the high-pressure shaft.