Washington:
An unmanned American experimental aircraft failed in a hypersonic test flight and dropped into the Pacific Ocean, the US Air Force said on Wednesday.
The aircraft, named X-51A Waverider, failed in its bid to reach a speed of Mach 6 (about 7,300 km per hour) on Tuesday, Xinhua reported.
The air force said the craft successfully separated in mid-air from a B-52 bomber served as mother ship, and the rocket booster fired as planned.
About 16 seconds into the test flight, a fault was identified with one of the cruiser control fins.
"It is unfortunate that a problem with this subsystem caused a termination before we could light the scramjet engine," said Charlie Brink, X-51A program manager.
The X-51A Waverider, or scramjet, was designed to fly for 300 seconds, and it was the third attempt by the air force at getting an X-51A airframe to go hypersonic.