One of the ongoing controversies plaguing the F-35 has been what powers it. There was early backing for two engines to be developed but Congress angrily quashed that in favour of but one, Pratt & Whitney's F-135 power plant.
Now the P&W backers, including Senator Joe Lieberman, are up in arms over a project underway by GE and Rolls Royce, the privately funded F-136 Adaptive Engine Technology Development project. The AETD option is gaining support at the Pentagon because of its promise to deliver 25% better fuel economy. With the F-35 already coming under criticism because of its poor range performance, the AETD engine would seem just the ticket. But to P&W and those in its pocket, the new engine is an enormous threat, not to mention an inconveniently timed embarrassment.