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Officials have completed the root cause analysis on why an F-35 engine caused an aircraft to burn in June, and temporary fixes are underway, program executive officer Lt. Gen. Christopher Bogdan said. As he’d previously expected, compressor blades rubbed too tightly against a polyimide seal, causing overheating, which cracked and broke the blades. “The short-term fix,” he said, is to “burn in” some engines by flying a “very specific profile” over two one-hour sorties per aircraft, which will cut a deeper blade trench in the seal material. Another fix will be to “pre-trench” the seal to prevent the rubbing. “Now through the end of December” all 19 test aircraft will receive one of the two fixes and get back up to a full flying schedule. To make up the lost flight test time, Bogdan told reporters on Oct. 30 the services have promised to fly a wartime-like “surge” to rack up flight tests, getting back to where the program should be by late January. A permanent fix, out of five options, will be chosen in the coming weeks, but Pratt & Whitney, maker of the F135 engine, will bear all the costs of the temporary and permanent fix, Bogdan said. New engines with the corrective changes will be produced starting at the end of 2015; the government will have to cover the non-recurring development costs.