General Electric and Rolls-Royce's decision to abandon their fight for an alternate engine to power the F-35 Joint Strike Fighter finally put an end to a long, politically charged battle with incumbent Pratt & Whitney. Or did it?

No, the GE-Rolls F136 is not rising from the dead. But a U.S. Air Force demonstrator program, in which GE, Rolls and Pratt are competing separately to develop fuel-saving propulsion technology for combat aircraft, could conceivably produce an alternate engine sized for the JSF as early as 2020. That possibility has sent jitters through Pratt and its allies on Capitol Hill.

The issue surrounds the adaptive engine technology development (AETD) program, a new effort that is rapidly gaining traction within the Pentagon because of its potential to save up to 25% in fuel burn over state-of-the-art engines. The Pentagon—which actively opposed the F-35 alternate engine plan for five years—supports the initiative run by the Air Force Research Laboratory (AFRL) and sees it as a key part of an energy-saving strategy to keep the Air Force's annual fuel use below 2.4 billion gal.

Sensing the longer term threat, Joseph Lieberman (I-Conn.), the senator most associated with the moves to counter the F136, is leading efforts to limit any possible impact of AETD on the F-35. But Lieberman, who leads the Senate Armed Services air-land subcommittee in charge of tactical aircraft, says he will not stop the Pentagon program aiming to develop engines that vastly improve fuel efficiency.

Despite these reassurances, according to insiders, military planners are taking a dim view of what they consider political attempts to emasculate the evolution of U.S. combat engine technology for the benefit of an incumbent manufacturer. However, of more concern to Pratt is that Deputy Defense Secretary Ashton Carter—a past critic of the company's F135 program—is thought to have asked AFRL to outline provisional schedules for making a production-standard engine available as early as 2020. This is well within the extended procurement schedule of the F-35, and early enough to make a significant impact on the production run of the F135.

Yet the Air Force officially downplays any suggestion of either linking the AETD directly to the F-35 or accelerating its development to make it a possible contender before the early 2020s. Testifying to Congress earlier this year, Steven Walker, deputy assistant secretary of the Air Force for science, technology and engineering, said the official target for AETD is for “follow-on final design, engineering manufacturing development [EMD], and ground and flight-test qualification of a production-ready engine early in the next decade for integration into legacy and future aircraft systems.”

The Pentagon has requested $214 million for the AETD in fiscal 2013. Lieberman would not divulge the details of the subcommittee's just-completed draft of the fiscal 2013 defense authorization bill, but says he is trying to “put some parameters” around the program. “I'm going to do everything I can, not to stop this program, but to make sure that it doesn't become a second engine, because that would be a waste of taxpayer money.”

The Air Force—which is understood to have conducted a low-level study projecting the cost savings in the F-35 if an AETD-based engine were used—defends the project and insists the focus is on future developments. During a subcommittee hearing this month, Lieberman asked Lt. Gen. Janet Wolfenbarger, military deputy at the Office of the Assistant Secretary of the Air Force for Acquisition, whether the advanced engine program was indeed an effort to resurrect a competing engine.

“No, sir, it is not,” Wolfenbarger told him, adding that the program is trying to capitalize on advances in AFRL's Advent (adaptive versatile engine technology) initiative. “This engine could be used in a whole host of platforms should it ever reach the point of being a development program. Right now it's just a question of ensuring that we are ready to go, should we as an Air Force decide that we want to embrace this opportunity to really reduce the fuel consumption in future generations of strike aircraft, bomber aircraft [and] tactical aircraft.”

The demonstrator builds on Advent, which has been developing a suite of technologies for variable-cycle architectures to reduce fuel consumption by up to 25% and increase range by 30%. Advent architectures add a third stream of relatively cooler air flow, in addition to the standard high-pressure core flow and second stream of bypass air. The third stream is used for high power extraction and better thermal management; it also reduces installed drag and improved inlet recovery. The cooler air mass can also be mixed with the outlet flow to reduce exhaust system temperatures and infrared signature.

AETD will go even further in terms of better efficiency and power, and take the Advent concept to a pre-full-scale EMD level. Unlike the smaller cores used in the initial Advent effort, the AETD engines will be built around a larger core theoretically sized to enable future projects—such as the U.S. Navy's F/A-XX and Air Force's F-X sixth-generation fighters—to supercruise, or fly supersonically without afterburner. The size requirement also happens to match that of the F-35.

Responses to AFRL's request for proposals are due May 31 and cover Phase 1 contracts that will be awarded in August for two rival engines. This will include initial concept evaluations by February 2013, compressor rig tests in 2014, fan and core tests by mid-2015 and full engine tests as early as 2016.

GE and Rolls, which are competing against each other in the Advent program, are submitting variable-cycle growth concepts for the AETD. GE, aiming to run the first full Advent engine late this year or early 2013, says it “has been approached by Senate and House defense appropriators regarding AETD funding because they are highly interested in the program's fuel-efficiency goals and timetable, and whether they are both achievable. We believe they are achievable based on our Advent efforts over the past five years. AETD will be a sporty competition for the three engine makers.”

NOTE: Story has been edited to reflect that Ashton Carter's criticism of the F135 program was expressed during the debate over the competitive engine.