The US Air Force has contractually re-opened the door for GE Aviation to challenge Pratt & Whitney for a potential propulsion upgrade for the Lockheed Martin F-35.

Both companies received separate $1 billion deals in early July to complete detailed designs of rival versions of an adaptive cycle engine, which includes a fuel-saving mode in cruise flight that can extend the range of a fighter by 20% to 30%.

Both deals also include priced options that, if exercised, could have GE and P&W run competing adaptive cycle engines in an F-35 after 2021, says Jean Lydon-Rogers, president of GE military engines. P&W also confirms receiving the same priced option in the contract awarded under adaptive engine transition programme (AETP).

The deals give GE an opportunity to re-enter the F-35 programme six years after Congress ordered the US Department of Defense to cancel the company’s F136, which was being developed as an alternate engine to the P&W F135.

The USAF launched the AETP programme to develop a next-generation engine for future combat aircraft, including a notional concept for a Lockheed F-22 replacement after 2030. Ongoing analyses for the so-called sixth-generation fighter includes a wide range of options, including a major upgrade of the F-35.

“One of the reasons we’re doing those technology programmes is for the possibility of an upgrade to the F-35,” says Frank Kendall, undersecretary of defense for acquisition, technology and logistics, speaking to journalists on 10 July in London.

GE has participated in the USAF’s adaptive cycle engine development efforts since 2007, keeping the company’s military engine technology up to date as P&W fields hundreds of F135 engines and develops an undisclosed propulsion system for the Northrop Grumman B-21 bomber.

“The other thing we see for the [US] Air Force as an advantage is we need to continue to advance our industrial base in those areas and our technology in the propulsion systems,” says Lt Gen Arnold Bunch, military deputy for the assistant secretary of the air force for acquisition.

An adaptive cycle engine is intended to save fuel in engines designed for high speed and fast acceleration. A conventional supersonic engine uses a minimum of fuel-saving air flow bypassing the engine core. An adaptive engine opens a second stream of bypass air flow in cruise flight, allowing the aircraft to reduce fuel burn while not rapidly accelerating or taking-off.

The USAF kicked off development of the adaptive engine programme in 2007 with GE only. In 2012, P&W and GE were both selected to continue development under the adaptive engine technology development programme. The award of the AETP contracts last will bring both companies to close to a final design of a new engine with adaptive cycle technology.