Air Force's Hypersonic X-51A jet fails latest test flight, is lost over the Pacific

After approximately 15 seconds of flight, the experimental aircraft designed to fly at six times the speed of sound was unable to maintain control during a test run Tuesday and was lost, the Air Force said in a statement.

The unmanned X-51A WaveRider was expected to reach Mach 6 after it was dropped by a B-52 bomber off the Southern California coast near Point Mugu, but a faulty control fin compromised the flight.

"It is unfortunate that a problem with this subsystem caused a termination before we could light the Scramjet engine," Charlie Brink, the X-51A program manager, said in a statement. "All our data showed we had created the right conditions for engine ignition and we were very hopeful to meet our test objectives."

Engineers hoped the aircraft would sustain its top speed for five minutes, twice as long as it’s gone before.

The Waverider successfully detached from the B-52 and fired the rocket booster as planned. Then its scramjet engine was supposed to take over as it attempted to climb to Mach 6. But that never happened. Fifteen seconds after separating from the rocket booster, the Waverider lost control, preventing a test of the scramjet engine.

"All our data showed we had created the right conditions for engine ignition and we were very hopeful to meet our test objectives," Brink said.

The Pentagon has been testing hypersonic technologies in hopes of delivering strikes around the globe within minutes. The jet is designed by Boeing Co.

Last year, in its most recent test, the X-51 fell for about four seconds before its booster rocket ignited, but the aircraft failed to separate from the rocket and plunged into the ocean.

During the first flight of an X-51A in 2010, it reached near five times the speed of sound for three minutes.

Program officials said they will evaluate the exact cause of the latest failure. Only one of the four X-51A vehicles remain, and officials have not decided when or if that vehicle will fly at this time, the statement said.

The Associated Press contributed to this report