(Adds details, background, Lockheed statement, byline)
By Jim Wolf
WASHINGTON Dec 17 Nearly a fourth of the U.S. Navy's fleet of Lockheed Martin Corp (LMT.N) P-3C Orion surveillance planes, some used in the U.S.-declared global war on terrorism, are being grounded due to fears of "structural fatigue," the Navy said on Monday.
It said 39 of the 161 planes in the P-3C fleet were affected, with repairs expected to take 18 to 24 months per plane.
"Program officials determined that these aircraft are beyond known structural limits on the lower section of the P-3 wing," the Naval Air Systems Command said in a statement.
No physical event was behind the grounding of P-3Cs, said John Milliman, a spokesman for the command based at Patuxent River, Maryland.
"This is data-driven," he said, referring to a continuing engineering analysis started in December 2004 to anticipate components' growing risk of failure.
The grounding is the latest for aging U.S. warplanes used heavily in post-Sept. 11 operations, including in Iraq and Afghanistan.
The Air Force grounded all its older-model F-15 fighter jets earlier this month for the third time in four weeks after stepped-up inspections found more metal fatigue.
Enhanced Air Force inspections began after the Nov. 2 crash of a nearly 30-year-old Missouri Air National Guard F-15C on a routine training flight.
The P-3C has been a key Navy maritime patrol aircraft since the 1960s. It is a land-based, four-engine turboprop designed for long-range maritime patrol, anti-submarine warfare and surveillance missions.
In recent years, its missions have expanded to include reconnaissance over conflict zones in Iraq, according to a Navy fact sheet.
In its statement, the Navy said 10 of the newly grounded aircraft had been deployed until now but did not say where. It said a decision was pending on whether to retire some of the planes permanently.
The Navy plans to purchase 108 P-8A Poseidon aircraft being developed by Boeing Co (BA.N) to replace its aging P-3 fleet. A Pentagon decision on full-rate production of the P-8A is expected in 2013, according to a Boeing fact sheet.
Milliman said the grounding was unlikely to have any impact on the timetable for acquiring P-8As.
The Navy expects to be able to fly P-3s until 2019, as currently scheduled, given fleet management precautions being taken, he said.
Lockheed Martin said it would do anything it could to help the Navy find a solution to the challenge.
"As the original equipment manufacturer, we are uniquely qualified to offer our assistance," said Thomas Jurkowsky, a company spokesman. "Besides the Navy, nobody knows this airplane better than Lockheed Martin." (Reporting by Jim Wolf; editing by John Wallace)