The Air Force should continue funding research and development on a new advanced engine for the F-35A Lightning II -- even if it ultimately scraps the work and sticks with the fighter jet's current engine, Gen. Charles "CQ" Brown, the service's chief of staff, said Wednesday.
The research could result, at least in part, in an improvement in fuel efficiency for the jet, known as the Pentagon's most costly weapons program ever. But Brown said the Air Force eventually will face a "fork in the road" and must decide whether to move forward on a completely new replacement engine.
Congress is concerned about the issue, and the House Armed Services Committee last week passed a defense policy bill for 2022 that would require the Pentagon to explain how it will put a better engine in the F-35A, which is the jet variant used by the Air Force.
"You've got to continue the R&D in certain areas so, that way, you have the options in the future," Brown said during an online panel Wednesday hosted by Defense News at its annual conference. "If we stop the R&D on this, we basically shut ourselves off from having an option to go forward."
The service has contracts with General Electric Aviation and Pratt & Whitney, through the Adaptive Engine Transition Program, to develop a new F-35A engine with improved fuel efficiency and more thrust, but it also could upgrade the F-35's current F135 engine.
The two defense contractors each won contracts worth $1 billion in 2016 for the program.
The Air Force has the most common F-35 variant, but the Navy and Marine Corps also fly versions of the aircraft, which is expected to cost $1.27 trillion over its 66-year lifespan, the Government Accountability Office reported in July.
Brown said he supports proposals in the policy bill that push the Pentagon to report sustainment costs of the F-35 and limit how many of the aircraft the military could buy, based on how well the services are keeping costs down.
"One of our goals is to make this sustainment [of the F-35] affordable," he said. "What's laid out by the Congress in this regard is exactly what we're trying to get done."
Meanwhile, Brown also said new delays in fielding the Air Force's next trainer aircraft aren't a significant problem.
The Air Force is working with contractor Boeing on the T-7 Red Hawk, which will replace the decades-old T-38 Talon and be used to train fighter and bomber pilots. Testing found a problem with "wing rock" that risked causing an uncontrollable roll.
"There are some areas, as we were going through some of the testing, that we found a couple of things," Brown said. "And that's somewhat typical as you bring [new airplanes] into the system. ... It is a slight slip, but nothing I would consider dramatic."
Brown told lawmakers in June that technical issues delayed the "Milestone C" review needed for the aircraft to go into full production. The decision on the T-7 now could happen in late 2023, more than a year after it was originally expected, though Boeing thought the delay would be several months shorter.
The delay led the service to cut its funding request for research and development on the T-7 in fiscal 2022 from $206 million to $189 million.