Guy Norris and Graham Warwick Fort Worth

Amassing flight hours and test points at an accelerating pace, the F-35 Joint Strike Fighter program faces the question of whether it is completing the right tests at the right time. As it enters 2013 with a focus on high angle-of-attack and weapons testing, the program is still falling behind in clearing the capabilities its customers require.

Lockheed Martin exceeded its development flight-test goals for 2012. But a report by the Pentagon's director of operational test and evaluation (DOT&E) reveals this was helped by bringing forward test tasks from future years. Aircraft deficiencies and software delays prevented the program from achieving some test objectives set for 2012 and required to deliver capabilities to the services now beginning to train pilots on the F-35.

Lockheed says it logged 1,167 flights and 9,319 test points in 2012, against the plan of 988 flights and 8,458 points. Of the flights completed, 926 were by flight-sciences test aircraft expanding the flight envelopes of the three F-35 variants, while 241 were by the smaller number of mission-systems aircraft assigned to testing avionics and sensors.

But according to the DOT&E report, through November 2012, the program had completed only 78% of the test points planned for the year. The addition of test points to investigate new problems, for regression testing of aircraft and software fixes, and for tasks brought forward from future years pushed the test points accumulated to 35% above the total planned (see F-35 Flight Testing table).

The report says horizontal-tail scorching and delamination and higher than expected airloads on open weapons-bay doors has restricted testing of all variants. Afterburner operating restrictions and delayed aerial-refueling disconnects have affected the conventional-takeoff-and-landing (CTOL) F-35A. Testing continues on a redesigned clutch, driveshaft and doors for the short-takeoff-and-vertical-landing (Stovl) F-35B, and the tailhook is being redesigned for the F-35C carrier variant (CV).

Sustained-maneuver and transonic-acceleration performance has been reduced for all three variants based on flight-test results, the DOT&E says. And live-fire ballistic testing has confirmed vulnerabilities resulting from the 2008 decision to delete shutoff systems for the flammable avionics coolant and nozzle fueldraulic actuation systems to save weight, the report reveals.