Lockheed Martin plans to resume flight-testing the first F-35 Joint Strike Fighter in August after a complete audit of the aircraft's electrical system was launched following a brief power failure on its last flight in early May.

The fault was caused by a short in the F-35's 270V power system when a lead inside a box touched the lid. "It was a short-duration event and the system responded exactly as it should," says air vehicle team lead Bobby Williams.

The power-by-wire flight-control system locked the affected surface - the right horizontal stabiliser - and adjusted the authority on the other control surfaces to compensate. "If the pilot had not known he had a fault, he would not have been aware of it from a flying qualities standpoint," says Williams.

The fault affected both branches of the power system where they come together to drive the stabiliser, but did not propagate outside the box to affect the rest of the aircraft, he adds.

Lockheed has completed a review of close-tolerance spacing in the aircraft's electrical system. "We have done a thorough audit of the 270V electrical power system to get the right spacing," says Williams. "Now we are going into each of the boxes on the aircraft to take a look at the tolerances. We will be back into flight in August."

The aircraft is undergoing scheduled upgrades while it is on the ground. "We are installing additional instrumentation, including inlet rakes, and doing additional proof testing, including the refuelling receptacle so we can start aerial refuelling," says Williams. The first release of prognostic health management software is being loaded, plus upgrades to the flight control software resulting from the first 19 flights.

Lockheed, meanwhile, has begun final assembly of the second JSF - the first F-35B short take-off and vertical landing variant. Mating of the major airframe sections began in June at Fort Worth, Texas and the aircraft is scheduled to roll out in December and fly in May next year. The aircraft, BF-1, is the first with the "optimised" airframe redesigned to reduce weight.

Source: Flight International