By Andrea Shalal-Esa

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 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 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.

(Reporting by Andrea Shalal-Esa; Editing by Gerald E. McCormick and Richard Chang)