In late 1966, the FAA selected Boeing to be the prime contractor for the first U.S. SST. After initially considering, then shifting away from, a variable-sweep wing design, a full-scale engineering mockup of the (50-degree-sweep) fixed-delta-wing Model 2707-300 was unveiled in June 1970. With a capacity of more than 300 passengers and a speed of Mach 2.7 (1,800 mph or 2,900 kilometers per hour) at 65,000 feet (19,700 meters), the Boeing SST would have been faster and have carried more passengers than the British/French Concorde SST. That passenger load would have helped airlines achieve a more favorable balance sheet. Unfortunately, Congressional concerns about SST program expense and environmental effects resulted in its cancellation on March 24, 1971.