An unmanned experimental aircraft designed to fly at six times the speed of sound broke apart over the Pacific Ocean seconds into a military test flight due to a faulty control fin, the US Air Force said.
The problem with the fin on the aircraft known as the Waverider or X-51A was identified in a test flight on Tuesday, 16 seconds after a rocket booster on the remotely monitored craft was ignited to propel it forward, the US Air Force said on Wednesday.
Fifteen seconds later, when the X-51A separated from the rocket booster, it lost control due to a "faulty control fin". The 31 seconds of flight fell far short of the military's goal for the X-51A to fly for five minutes.
The aircraft broke apart immediately and fell into the Pacific Ocean near Point Mugu northwest of Los Angeles, said Daryl Mayer, a spokesman for the 88th Air Base Wing at Wright-Patterson Air Force Base in Ohio.
Even if the test had been a success, the aircraft would have crashed at the end of the flight in any case and was not considered retrievable.
The Waverider was designed to reach speeds of Mach 6 or above, six times the speed of sound and fast enough to zoom from New York to London in less than an hour.
The military has its eye on using the Waverider programme to develop missiles with non-nuclear explosives that could strike anywhere in the world within an hour, analysts say.
The cost of the X-51A, which officials said was dropped from a B-52 bomber before its rocket booster was ignited, has not been disclosed because many details of the programme are classified.
The aircraft is known as the Waverider because it stays airborne, in part, with lift generated by the shock waves of its own flight. Boeing's Phantom Works division performed design and assembly on the craft, the military said.
Boeing declined to comment on the test flight, citing an Air Force request to have all public communication come from the military.
This was the third of four X-51A aircraft built for the military, one of which flew for more than three minutes at nearly five times the speed of sound during a 2010 test flight, the air force said.
The air force, which is analysing data from Tuesday's test flight, said one X-51A aircraft remains.