(Adds Pentagon and Honeywell representatives' comments, background)
By Andrea Shalal-Esa
WASHINGTON Feb 25 (Reuters) - The Pentagon said on Monday an F-35 test plane was involved in an incident on Feb. 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 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. Interim changes had been implemented 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.
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 Feb. 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 Feb. 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 the Boeing plane on Jan. 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 safe after extensive testing.
Hawn said an initial assessment of the Feb. 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 auxiliary power unit's hardware.
The whole 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 and fix any such problems.
"This is the purpose of test, development & initial training in any program; identify discrepancies, develop fixes, and put them in place to ensure safety of operations," she said. "Engineering assessment of issue indicates minimal risk, and (a) relatively uncomplicated resolution."
Honeywell spokesman Nathan Drevna said the company was aware of the Feb. 14 incident and would inspect the system carefully once it arrived at the company's testing 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. (Reporting by Andrea Shalal-Esa; Editing by Gerald E. McCormick and Richard Chang)