The document discusses the design and power transmission system of an advanced light helicopter. It describes the four main gearboxes - the main gearbox, auxiliary gearbox, intermediate gearbox, and tail gearbox. The main gearbox increases torque and reduces speed from the engine before transmitting power to the other gearboxes. The auxiliary gearbox cools the main gearbox oil before transmitting power to the intermediate gearbox. The intermediate gearbox redirects the driveline upward at a 125 degree angle to the tail gearbox. The tail gearbox then drives the tail rotor blades to provide counteracting thrust. Shims are used between gears in the gearboxes to achieve the proper gear mesh patterns and backlash during assembly given manufacturing variations in part