By Andrea Shalal-Esa
WASHINGTON (Reuters) - The Pentagon said on Wednesday that no additional cracks have been found on F-35 fighter engines during inspections begun after the February 19 incident that halted flights of the entire fighter fleet, and operation of the engines on the ground.
Kyra Hawn, spokeswoman for the F-35 program office, said officials were continuing to investigate a cracked engine blade found on a test plane at Eglin Air Force Base in Florida, with engineers at enginemaker Pratt & Whitney due to break open the affected engine blade for further study on Wednesday.
Pratt, a unit of United Technologies Corp, supplies the engine for the single-engine, single-seat fighter plane, which is built by Lockheed Martin Corp.
The Pentagon announced the grounding of all F-35 warplanes on Friday after an inspection revealed a crack on a turbine blade in the jet engine of an F-35 being tested at Edwards Air Force Base in California.
It was the second engine-related grounding in two months of the $396 billion F-35 Joint Strike Fighter, the Pentagon's largest weapons program. The Marines Corps version of the plane was grounded for nearly a month starting in mid-January because of a faulty hose in the engine.
Hawn said inspections were under way of the engines on all 51 F-35 jets in the Pentagon's inventory, as well as additional engines that are spares or on planes being assembled by Lockheed at its Fort Worth, Texas, plant.
None of the engines inspected thus far had shown similar cracks to the one found on the Florida test plane, she said.
She said nondestructive testing of the cracked turbine blade had been completed, including microscopic tests and X-rays, with additional "destructive" testing scheduled for Wednesday, including a test in which the blade will be "fractured" open for closer examination of the surface.
She said the Pentagon would announce further details when the engineering investigation was complete.
Sources familiar with the investigation told Reuters on Tuesday that Pratt & Whitney is 99 percent sure the problem with the turbine problem that grounded the Pentagon's F-35 fleet was not caused by high-cycle fatigue, which could force a costly design change.
Pratt officials have also largely ruled out a manufacturing defect, according to two sources briefed on the investigation, who said the company was recommending the resumption of ground operations of the engine as early as Wednesday, and a return to flight operations later this week.
Tests completed on Tuesday supported that view, pointing to a "creep structure rupture" caused by the fact that the engine on that particular test plane had been run particularly hard at hot temperatures since it was used for after-burner testing, said the two sources, who were not authorized to speak publicly.
Current engines would not reach the same "hot time" for years, Pratt engineers have said, which would allow the Pentagon to impose incremental limits on engine use and monitor them for possible component replacement, one of the sources said.
"Basically this engine was run for an extraordinary amount of time at very high power in a short period of time," said the source, who was not authorized to speak publicly.
Pratt had no comment on the state of the investigation.
The top uniformed officers in the Air Force, Navy and Marine Corps are due to meet on Thursday for a long-scheduled meeting about the F-35, but they are slated to discuss bigger issues such as when the services can start using the new warplanes for military operations, according to a defense official familiar with the meeting. The services must provide estimated dates for "initial operating capability" to Congress by June 1.
The service chiefs would also discuss a new Pentagon drive to use competition to reduce the staggering cost of operating and maintaining the new jets, a sum now forecast at over $1 trillion over the next decades, the source said.
Lieutenant General Christopher Bogdan, who runs the F-35 program for the Pentagon, slammed Pratt and Lockheed during an air show in Australia earlier on Wednesday, accusing the companies of trying to "squeeze every nickel" out of the U.S. government and failing to see the long-term benefits of the project.
Hawn said a separate incident involving temperature control equipment built by Honeywell International Inc has been deemed a "minor test discovery, with no impact to safety of flight or operations.
(Reporting by Andrea Shalal-Esa; editing by Gerald E. McCormick, Matthew Lewis and Bernard Orr)