Air Force photo / Master Sgt. Jeremy T. Lock An F-35A at Eglin Air Force Base, Fla., is readied for flight.

There’s a new and disquieting Pentagon report on the troubled $400 billion tri-service F-35 fighter.

It includes stunning pilot comments about the aircraft’s survivability (“Aft visibility will get the pilot gunned [down] every time”) while detailing the limited performance of the Air Force’s F-35A and its support systems during initial training at Florida’s Eglin Air Force Base.

The chief Pentagon weapons-tester’s 68-page report, posted at the Project on Government Oversight’s website here, describes the challenges Air Force pilots must accept to train in the aircraft. CliffsNotes‘ summary, here.

Some of the shortcomings are simply a result of the immature state of the F-35, even though the program is more than 10 years old. However, there are also issues that will never be solved, and there are unknowns about whether the F-35 will ever perform up to its modest specifications.

Those answers won’t be known until 2019, when operational testing is currently scheduled to be wrapped up — assuming everything goes perfectly from here on out.

As of now, the F-35As at Eglin Air Force can do little more than burn non-supersonic holes in the sky, using only gentle stick maneuvers and hardly any of the F-35’s highly-complex electronics.

Perhaps the biggest horror story is the poor showing of the Lockheed plane’s complicated, expensive helmet-mounted display system that distorts and obscures – rather than enhancing — the pilot’s vision and awareness of the outside world.

That, along with the poor design of the ejection-seat headrest and limited visibility outside the cockpit, gave rise to that pilot’s warning that the F-35A can easily be “gunned” from the rear in visual range air-to-air combat — the type that historically has dominated fighter encounters.