Pratt & Whitney has lost out in a competition to demonstrate the next generation of propulsion system for the US Air Force, prompting questions about the future of its fighter engine business.

General Electric and Rolls-Royce have won contracts to build variable-cycle ground demonstrators under the US Air Force Research Laboratory's Adaptive Versatile Engine Technology (Advent) programme.

R-R describes the win by its US LibertyWorks research unit as "strategic" as the company has not before built a clean-sheet high-thrust engine, previously teaming with GE. The two companies are developing the F136 alternative engine for the Lockheed Martin F-35 Joint Strike Fighter, but bid separately for Advent.

P&W is "disappointed by AFRL's decision", but says it will continue to work to find opportunities to use its technologies. The company is producing the F119 powering the Lockheed F-22 and developing the F135 for the F-35, but Advent is seen as the next generation of military engine.

GE has received $231 million and R-R $296 million to demonstrate variable-cycle engines that combine low bypass ratio and high thrust for supersonic dash with high bypass ratio and low fuel consumption for subsonic loiter, possibly using a second fan flowpath.

R-R has a different approach to GE, says Dennis Jarvi, president, defence North America. "The key is our ability to manage clutches and airflow. We have come up a credible concept to make a variable engine viable for the first time," he says. "We have to do variable cycle to get a step change in performance."

If rig tests in 2009 are successful, full engine runs are planned for 2012. AFRL says the Advent engine will not be ready for the USAF's next-generation bomber in 2018, "but if that slips to 2020-22 it becomes realistic", says Jarvi. "It could be worth waiting a couple of years for this."