The F-35 Lightning II test aircraft are authorized to fly again, program officials announced Thursday, after the fleet was grounded following an onboard fire earlier this month. Air Force and program officials still haven't nailed down the exact cause of that fire, which started in a test jet's Integrated Power Package, but they're confident it's safe for the rest of the test F-35s to return to flight status even as engineers continue investigating.
The Air Force's two production aircraft, however, stationed at Eglin AFB, Fla., will remain grounded until program officials arrive at a final fix for the aircraft's problems.
Here was the official word:
An Air Force Safety Investigation Board continues to review the circumstances that led to the failure of an Integrated Power Package (IPP) aboard AF-4, an F-35A conventional takeoff and landing variant assigned to Edwards AFB, Calif., on August 2. The F-35 Integrated Power Package is a turbo-machine that provides power to start the engine and generates cooling for the aircraft. The government and contractor engineering teams determined the program could resume developmental test flight operations while the investigation continues. This assessment was made after reviewing data from ground and flight tests which showed, with revised test monitoring procedures governing the IPP, the aircraft can be flown safely.
The root cause investigation indicates that an IPP valve did not function properly. Monitoring of valve position is a mitigating action to allow monitored operations. A permanent resolution is in work.
The return to flight has been authorized for all aircraft assigned to Edwards AFB and Patuxent River Naval Air Station, Md. This does not allow ground operations for Eglin AFB, Fla. delivered aircraft (AF-8, AF-9). The completion of the root cause investigation and any corrective actions are required to return to unmonitored operations.
Impact to System Development and Demonstration test flight execution and production operations continues to be assessed. The program, however, has built margin into the test schedule to accommodate incidents that occur in the development effort.