The A330 and A340 fuselage is based on that of the Airbus A300-600, with many common parts, and has the same external and cabin width: and . Typical seating arrangements are 2–2–2 six-abreast in business class and 2–4–2 eight-abreast in economy class. The fin, rudder, elevators, horizontal tail plane are used as fuel tank, flaps, ailerons and spoilers; they are made of composite materials, making 10% of the structure weight. When necessary, the A330 uses the Honeywell 331–350C auxiliary power unit (APU) to provide pneumatics and electrical power.