The Air Force says the second test of a hypersonic experimental aircraft ended in a crash off the Southern California coast earlier this week.

The Los Angeles Times reports Friday that a video shows the unmanned X-51 WaveRider crashing after it was successfully dropped by a B-52 bomber that had taken off Monday from Edwards Air Force Base.

The aircraft developed by Boeing Co. fell for about four seconds before its booster rocket engine successfully ignited, but the aircraft failed to separate from the rocket and plunged into the ocean.

Engineers are reviewing data to identify the cause of the problem.

The 14-foot aircraft, designed to hit 4,000 mph, is being developed to give the Pentagon a new way to deliver a military strike anywhere around the globe within minutes.