In the late 1990s, Boeing began considering a replacement for the 767 when sales weakened due to the competing Airbus A330-200. As sales of the Boeing 747-400 also slowed, the company proposed two new aircraft, which were the Sonic Cruiser and the 747X. The Sonic Cruiser would have achieved higher speeds (approximately Mach 0.98) while burning fuel at the same rate as the existing 767 or A330. The 747X, competing with the Airbus A380, would have lengthened the 747-400 and improved efficiency by using a composite supercritical wing.

Market interest for the 747X was tepid, but the Sonic Cruiser had brighter prospects. Several major airlines in the United States, including Continental Airlines, initially showed enthusiasm for the Sonic Cruiser concept, although they also expressed concerns about the operating cost. By decreasing travel time, they would be able to increase customer satisfaction and aircraft utilization.

The September 11, 2001 attacks upended the global airline market. Airlines could not justify large capital expenditures, and increased petroleum prices made them more interested in efficiency than speed. The worst-affected airlines, those in the United States, were considered the most likely customers of the Sonic Cruiser. Boeing offered airlines the option of using the airframe for either higher speed or increased efficiency, but the high projected airframe costs caused demand to slacken further. Boeing canceled the 747X once Airbus launched production of the Airbus A380, and switched tracks by offering an alternative product, the 7E7.

Copyright 2012