The first Lockheed Martin F-35A Lightning II (Joint Strike Fighter) has now been grounded for nearly six months. On its 19th flight in early May, the aircraft encountered an electrical arcing problem in the flight control unit of the right horizontal tail. The F-35 has a unique electro-hydrostatic actuation system. The problem has been fixed, but Lockheed Martin flight-test officials at Fort Worth, Texas, are still awaiting clearance to fly, after ground testing by F-35 partner companies revealed anomalies with the integrated power package and the short takeoff and vertical-landing version of the Pratt & Whitney F135 engine. Lockheed Martin officials recently told AIN they had accomplished planned software upgrades, and advanced other work, during the long downtime of the first F-35A. They also said that the F-35 flight-test schedule should not be unduly affected in the medium term by the unexpected delay, thanks in part to the role that will be played by the “CATbird,” a modified Boeing 737 that will test all five of the F-35’s avionics systems. It is being prepared for flight tests of the F-35’s communications, navigation and information system, starting next month. Meanwhile, another three airframes–the first and second F-35B aircraft and a static test vehicle–have entered final assembly. [F-35 Joint Strike Fighter program proceeds apace] AIN will report further on the F-35 flight test program in our on-site editions at the Dubai Airshow next month.