In order to produce the twin-engined Boeing 737 a new assembly line was built in 1966 at Renton and the plant is still building the Boeing 737 family. The 737 final assembly building when built was at the time the largest building in the world by volume. New aircraft perform their first flight from the adjacent Renton Municipal Airport and are then flown to Boeing Field for customer preparation. In 2011 after a lengthy negotiation, Boeing and the Machinist Union have agreed to produce the 737 MAX, a redesign, at the existing facility in Renton.