A power extraction system and method for a gas turbine engine of a vehicle are provided. The system has an HP spool tower shaft coupled between an HP spool of the gas turbine engine and an accessory gearbox assembly coupled to the gas turbine engine. The HP spool tower shaft extracts mechanical power from the HP spool. The system has an LP spool tower shaft coupled between an LP spool of the gas turbine engine and the accessory gearbox assembly. The LP spool tower shaft extracts mechanical power from the LP spool. The system further has the accessory gearbox assembly having an accessory drive combining the mechanical power from both the HP spool and LP spool, having a planetary gear train coupled to the accessory drive, and having one or more engine-driven accessories coupled to the planetary gear train and driven by a planetary gear train output to generate power.