A turbofan engine according to an exemplary embodiment of this disclosure includes, among other possible things, 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; 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, wherein the second tower shaft is engaged to drive the sun gear; a first clutch for selectively coupling the first tower shaft to the ring gear; a second clutch for selectively coupling the sun gear to the carrier; and an accessory gearbox driven by an output of the superposition gearbox.