A screwed-up control valve caused the grounding of the F-35 fleet and the program office has cleared the plane for ground operations while it tests the errant valve. Meanwhile, the F-22 fleet remains grounded until early fall when the results of an investigation into possible problems with the plane’s oxygen system are completed.

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The F-35 fleet was grounded August 3 after a valve in the Integrated Power Package (IPP) of aircraft AF-4 [pictured above] failed. The IPP is a a sort of super generator that provides power to start the engine and cools the plane.

The Joint Program Office which manages the F-35 program was clearly eager to let the public know that they’ve found the cause of the failure. But they were cautious about when a return to flight will occur.

“While initiating DT ground operations is a major step for the F-35 fleet returning to flight, further reviews are required prior to lifting the suspension of flight operations for the 20 F-35s currently in flying status,” JPO spokesman Joe DellaVedova said in a statement. “The impact to SDD execution and production operations is being assessed. The program has built margin into the test schedule to accommodate incidents that occur in the development effort.” So, keep your hats on and we’ll let you know when things are back to normal.

Meanwhile, I checked on the status of the F-22, which was grounded May 3 because of concerns that the plane’s oxygen system — crucial for the high-flying plane — was causing hypoxia in pilots. Air Force spokesman Lt. Col. John Haynes said no root cause has been found for the problem yet and none is expected until the safety board completes its investigation, expected in early fall.

In January, Air Combat Command issued an order that America’s top fighter fly below 25,000 feet after an F-22 crashed in Alaska. The pilot died in that accident, which apparently was not connected to the oxygen system.

While some news reports have claimed the nation’s stealth fighter fleet was grounded because both the F-35 and the F-22 were on the ground, that goes too far. The F-35 hasn’t been cleared for deployment yet so it doesn’t count as an operational plane yet. The $77.4 billion F-22 fleet (soon to be 187) certainly does count. While it hasn’t flown in anger yet, one does begin to wonder about the utility of a high-flying plane in service for some time that may sport a faulty oxygen system.