FORT WORTH, Texas, June 28 (UPI) -- All three versions of the U.S. Joint Strike Fighter have now cleared the final milestone needed before entering the production phase. The carrier version of the cutting-edge F-35 recently passed its Air System Critical Design Review, putting it on track for Low Rate Initial Production. The conventional and short-takeoff, vertical landing variants of the plane passed the CDR earlier and have been approved for LRIP. "The die is now fully cast for the unique, three-variant Joint Strike Fighter program envisioned when the planning began in the late 1990s," said Air Force Brig. Gen....