F-35 Engine Fix Coming, Program Chief Says

[nitpicker]

http://www.defense.gov/news/newsarticle.aspx?id=123543

F-35 Engine Fix Coming, Program Chief Says

By Claudette Roulo
DoD News, Defense Media Activity

WASHINGTON, Oct. 31, 2014 – The head of the F-35 Lightning II joint strike fighter program office said yesterday that he expects to have decided on a permanent solution by the end of December for the design issue that caused an engine to fail in June in an F-35A at Eglin Air Force Base in Florida. The engine's manufacturer, Pratt & Whitney, has offered several potential fixes, some of which already are being tested, Air Force Lt. Gen. Christopher C. Bogdan told reporters yesterday.
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The engine failure and subsequent fire were the result of micro fractures in one of the three-stage fan sections that compress air before it enters the engine, the general said.
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"Two short mid-term fixes have already been validated," Bogdan said.

For the first, a new engine is flown in a defined profile that subjects it to a specific set of altitudes, airspeeds, G-forces and roll rates, he said. "And in two sorties, you can burn in the engine in a very controlled way," the general said, "such that where this rubbing occurs has now been burned in, so to speak, and anything else you do with the airplane inside the envelope won't cause any more rubbing than what it has already seen."
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The second method involves a change to the manufacturing process of the engine, the general said. Instead of designing the blades to rub on the polyimide lining of the stator walls, the lining would be "pre-trenched," he said. "When we put the fan blade in there, no matter what we do on the airplane G-wise, speed-wise, altitude-wise, it won't rub anymore," the general said.
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Pratt & Whitney is bearing the cost of retrofitting or burning in all of the fielded engines, Bogdan noted. Two methods were needed because fabricating a set of new stators takes a week, Bogdan said. "So if we just went with that method alone,” he said, “it would take us quite a while to replace all the engine fan sections of the fielded airplanes. … With the rub-in procedure, we can start getting to the same result by flying those airplanes through the burn-in. That's why it's important to get both those solutions out there."

Pratt & Whitney has presented several options for a long-term solution to the issue,
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Bogdan said he estimates it won't be until near the end of 2015 before engines are coming off the production line with the chosen solution. Once that happens, he added, any engines that are not in airplanes yet will be retrofitted.