In case you haven't seen this yet, almost all F-35s have been cleared to resume flying. This comes roughly three weeks after a valve failure on test jet AF-4's critical (and revolutionary) Integrated Power Package grounded the fleet. While the program office hasn't yet determined the root cause of the problem, all F-35 test jets are cleared to fly as long as the valve position is monitored. The two production F-35s at Eglin Air Force Base in Florida won't be able to fly until the root cause is fully identified and a fix is implemented.
Here's what the program office has to say:
The F-35 Joint Program Office authorized the return to flight operations for F-35 developmental test aircraft. This follows the reinstitution of ground operations for these aircraft Aug. 10.
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 (CTOL) variant assigned to Edwards AFB, Calif. on August 2. The F-35's 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 approved 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 t0 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.