The U.S. Air Force flew a Boeing-built experimental hypersonic vehicle for over six minutes May 1 in what was the longest air-breathing hypersonic flight ever and the longest of the four X-51A test flights.

“It was a full mission success,” Charlie Brink, X-51A program manager for the Air Force Research Laboratory Aerospace Systems Directorate, said in a press release. “The X-51A Waverider will serve as the bedrock for future hypersonics research and ultimately the practical application of hypersonic flight.”

Officials from Boeing Defense, Space & Security of St. Louis were equally pleased.

“This demonstration of a practical hypersonic scramjet engine is a historic achievement that has been years in the making,” Boeing Phantom Works President Darryl Davis said in a press release. “This test proves the technology has matured to the point that it opens the door to practical applications, such as advanced defense systems and more cost-effective access to space.”

The vehicle left the Air Force Test Center at Edwards Air Force Base, Calif.,under the wing of a B-52H Stratofortress aircraft. At 15,000 meters, the vehicle was released, fueled by a solid-rocket booster, and then accelerated to Mach 4.9 in 26 seconds. The vehicle then separated from the booster, the scramjet engine lit and the vehicle accelerated to Mach 5.1 at 18,000 meters.

Because the vehicle had only a 240-second supply, it then splashed into the ocean over the Point Mugu Naval Air Warfare Center Sea Range.

In total, the vehicle flew 525 kilometers.

The Air Force weighed canceling the troubled test program last year after the third X-51A Waverider vehicle veered off course soon after separating from its carrier aircraft and crashed into the Pacific Ocean. The Aug. 14 failure marked the third X-51A test flight to end prematurely.

The Waverider is designed to achieve speeds in excess of Mach 5 — five times the speed of sound — on the power of a supersonic combustion ramjet engine, also known as a scramjet. Boeing built four X-51A vehicles under contract to the Air Force and Defense Advanced Research Projects Agency.

Until the May 1 flight, the last time the vehicle fully transitioned to scramjet-powered flight was in the first Waverider flight in May 2010. The scramjet engine ignited and failed shortly thereafter during the second flight, and never got a chance to ignite during the third.

Officials have said they expect the Air Force to conduct a follow-on program to “mature scramjet engine technology.”