A disclosed turbofan engine includes a first spool including a first turbine; a second spool including a second turbine disposed axially forward of the first turbine, a first tower shaft engaged to the first spool, a second tower shaft engaged to the second spool, and a superposition gearbox including a sun gear, a plurality of intermediate gears engaged to the sun gear and supported in a carrier and a ring gear circumscribing the intermediate gears. The 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 clutch selectively couples the first tower shaft to the ring gear and a second clutch selectively couples the ring gear to a static structure of the engine. An accessory gearbox is driven by an output of the superposition gearbox.