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WASHINGTON (Reuters) - The Pentagon said on Monday an F-35 test plane was involved in an incident on February 14 that caused smoke in the cockpit, and it was sending the affected parts back to their manufacturer, Honeywell International Inc, for a detailed inspection.
Kyra Hawn, spokeswoman for the $396 billion (261 billion pounds) F-35 Joint Strike Fighter program, said an initial assessment of the incident at a Maryland air base showed it was isolated, software-related, and posed minimal risk. The Pentagon has made temporary changes to prevent another smoke incident, she said.
News of the previously unreported incident comes just days after U.S. military officials grounded the entire fleet of Lockheed Martin Corp F-35 jets for the second time this year after discovering a 0.6 inch crack on a fan blade in the single jet of another test plane.
A spokesman for engine maker Pratt & Whitney, a unit of United Technologies Corp, said the blade assembly arrived at the company's Middletown, Connecticut, facility on Sunday evening and engineering teams were examining it now.
Honeywell builds the plane's "power thermal management system," which uses a lithium-ion battery similar to those whose failures have grounded Boeing Co's entire fleet of 787 airliners, but Hawn said there was no connection between the February 14 incident and the F-35's lithium-ion batteries.
"It has no linkage whatsoever with the lithium-ion batteries," Hawn said. She said the February 14 incident was the only one involving smoke in the cockpit of an F-35 "in recent program history."
Lockheed is building three models of the new radar-evading warplane to replace nearly a dozen fighter jets in use by the U.S. military and its allies. The Pentagon plans to buy 2,447 of the advanced fighter in coming decades.
Honeywell said it would inspect the system, which manages the distribution of hot and cold air in the F-35 fuselage, once it arrived at the company's Phoenix testing facility.
The U.S. Federal Aviation Administration grounded Boeing's 787 commercial airliner on January 16 after two separate battery failures, including one that triggered an emergency landing in Japan after the crew detected smoke in the cockpit.
Boeing's biggest rival, Airbus, a unit of Europe's EADS, has decided in the aftermath to skip using lithium-ion batteries in its new A350 airliner.
But the Pentagon earlier this month said it would continue using lithium-ion batteries on the F-35 since they were made by different manufacturers from those used on the 787, and had been found to be safe after extensive testing.
Hawn said an initial assessment of the February 14 incident involving BF-2, one of the Marine Corps' short takeoff, vertical landing variants, had linked the problem to a software issue, not a problem with the hardware on the auxiliary power unit.
The entire temperature management system was being sent to Honeywell for a closer inspection and development of a permanent fix, she said, noting that the plane was going through developmental testing specifically to find any such problems.
"This is the purpose of test, development and initial training in any program - identify discrepancies, develop fixes, and put them in place to ensure safety of operations," she said, adding that initial assessment indicated "minimal risk and (a) relatively uncomplicated resolution."
Honeywell spokesman Nathan Drevna said the company would inspect the system once it arrived at the Phoenix facility.
"The pilot landed safely. The Honeywell-related products are being shipped to our testing facility so we can quickly inspect and determine next steps with our customer," Drevna said.
Lockheed spokesman Michael Rein said there was no sign that a lithium-ion battery was involved, and the battery had not been pulled from the F-35 for further review. "There is no evidence that the lithium ion batteries are a contributor to this event," he said, adding, "no battery faults were observed at any time."
One U.S. defence official familiar with the incident said the F-35 pilot reported "trace amounts of smoke" in the cockpit after he followed procedures to stop and restart the auxiliary power unit when a caution light came on.
The pilot then halted the test flight and landed safely at the base, without ever declaring an in-flight emergency, said the official, who was not authorized to speak publicly, adding, "there wasn't any fire associated with the smoke incident."
Procedures have now been changed so that pilots do not restart the backup power unit in flight, the official said.
Honeywell's Drevna said the temperature control unit is part of a bigger integrated power package (IPP), also built by Honeywell, which uses a 270-volt lithium-ion battery to start the engine, and also provide emergency backup power. Only the temperature control system was being sent back to Honeywell.
Lockheed said the power and thermal system was not using the battery at the time of the February 14 incident and the battery checked out as fully functional during a post-flight review. The IPP also functioned as designed, he said.
A malfunctioning valve in the larger IPP system grounded the F-35 for two weeks in August 2011, but this was a separate issue, the Pentagon said on Monday.
Editing by Gerald E. McCormick, Richard Chang and Matthew Lewis