The airframe incorporates the use of composite materials, which comprise nine percent of its original structural weight (all models outside the 777-8 and 777-9). Elements made from composite material include the cabin floor and rudder. The main fuselage cross-section is circular and tapers rearward into a blade-shaped tail cone with a port-facing auxiliary power unit. The aircraft also features the largest landing gear and the biggest tires ever used in a commercial jetliner. The six-wheel bogies are designed to spread the load of the aircraft over a wide area without requiring an additional centerline gear. This helps reduce weight and simplifies the aircraft's braking and hydraulic systems. Each tire of a 777-300ER six-wheel main landing gear can carry a load of , which is heavier than other wide-bodies such as the 747-400. The aircraft has triple redundant hydraulic systems with only one system required for landing. A ram air turbine—a small retractable device which can provide emergency power—is also fitted in the wing root fairing.