A turbofan engine includes a first spool including a first turbine and a second spool including a second turbine. A superposition gear system includes a plurality of intermediate gears engaged to a sun gear and supported in a carrier and a ring gear circumscribing the intermediate gears. A second tower shaft is engaged to drive the sun gear. A starter is selectively coupled to the sun gear through a starter clutch. A first electric motor and a second electric motor are coupled to the superposition gear system and are operable to input power into a corresponding one of the first and second spools.