Dual spool power extraction with superposition gearbox

An auxiliary gearbox drive system for a turbofan engine, the auxiliary gearbox comprising:

• a sun gear, wherein the sun gear is configured to be coupled to a second tower shaft of the turbofan engine;
• a plurality of intermediate gears engaged to the sun gear and supported in a carrier;
• a ring gear circumscribing the intermediate gears;
• a first means for selectively coupling the ring gear to a first tower shaft of the turbofan engine;
• a second means for selectively coupling the sun gear to the carrier;
• and
• an output to an auxiliary gearbox.

A method of operating an auxiliary gearbox for a turbofan engine comprising:

• coupling a first tower shaft to engage a first spool;
• coupling a second tower shaft to engage a second spool;
• coupling a sun gear of a superposition gearbox to the second tower shaft, wherein the superposition gearbox includes the 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;
• and
• selectively coupling the first tower shaft to the ring gear and/or the sun gear to the carrier to generate a driving output to an accessory gearbox or a driving input to the second tower shaft.