Half-inch crack blamed for U.S. F-35 fighter jet grounding - sources
* Initial blade test results expected as early as Wednesday
* Engine blade sent to Pratt in Connecticut for detailed tests
* Officials opted for grounding until worst-case scenario ruled out
By Andrea Shalal-Esa
WASHINGTON, Feb 23 (Reuters) - The engine blade crack that prompted the U.S. military to ground all 51 F-35 fighter jets was over half an inch long, according to three sources familiar with the matter, but it remained unclear if the crack was caused by a manufacturing anomaly or some larger design issue.
Engineers at Pratt & Whitney, a unit of United Technologies Corp, will conduct a detailed examination of the turbine blade as soon as it arrives at the company's Middletown, Connecticut, site, said spokesman Matthew Bates.
"Pilot safety is our absolute top priority," Bates said, noting that the F135 engine that powers the new radar-evading fighter jet had a readiness rate of over 98 percent.
"We are in a testing phase of the program and discoveries such as this are part of the process," he added.
Initial results may come on Wednesday, although it could take up to 10 days to complete the analysis, said the three sources, who were not authorized to speak publicly.
The Pentagon announced the grounding of all F-35 warplanes on Friday after an inspection revealed a crack on a turbine blade in the Pratt-built jet engine of an F-35 jet being tested at Edwards Air Force Base in California.
It was the second engine-related grounding of the $396 billion F-35 Joint Strike Fighter in two months, and came on the eve of a big air show in Australia, which is considering reducing its planned purchase of 100 F-35 jets.
The Pentagon's top F-35 official and executives from prime contractor Lockheed Martin Corp are attending the air show in hopes of convincing Australia that the F-35 program is on track after three restructurings, and Australia does not need to buy 24 more Boeing Co F/A-18 Super Hornets.
Australia is expected to make a decision within the next three to six weeks, said a fourth source familiar with the matter. The program is also bracing for reductions in U.S. orders if Congress fails to avert across-the-board cuts due to take effect on March 1.
Inspectors found an anomaly on Feb. 19 during an inspection that is conducted on every F-35 engine after 50 flight hours, but the crack on the blade was not confirmed until early Thursday after electromagnetic testing that began Wednesday and continued through the night, said one of the sources.
The crack was described as 0.6 inches (1.5 cm) long, the sources said.
F-35 test and training flights continued until Thursday evening, when the Pentagon's F-35 program office, the U.S. Navy and Air Force decided to suspend all flights and ban use of the engines on the ground until the blade crack was better understood.
In fact, two jets were airborne at air bases in Maryland and Arizona and had to be recalled, said one of the sources.
Officials decided that they had to assume a "worst case scenario" until they could rule out a high-duty cycle fatigue crack, an extremely rare occurrence that could result in a complete blade failure in just 90 minutes, the source said.
Engineers did not believe that this case involved such a devastating crack, but officials opted to take a conservative approach to ensure safety, the source said.
Colonel Kevin Killea, who oversees aviation acquisition for the Marine Corps, said that while the grounding was frustrating for test pilots and trainers, it was prudent. He added that finding problems was an expected part of developing any aircraft.
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