By Doug Cameron
The Pentagon on Thursday said much of the global fleet of Lockheed Martin Corp. F-35 combat jets was temporarily grounded to investigate engine problems that may have caused a Marine Corps plane crash last month.
Officials said the fleet of about 320 jets would undergo inspections over the next 48 hours to check fuel tubes in engines that are made by Pratt & Whitney, a unit of United Technologies Corp.
The suspect tubes may be installed on around half of the global fleet, limited to planes made before 2016, according to people familiar with the F-35's production process. Some aircraft have already been inspected and have resumed flying.
"If suspect fuel tubes are installed, the part will be removed and replaced," said the F-35 Joint Program Office, which oversees the purchase and operation of the planes.
The Pentagon in recent months has said parts shortages and a backlog of maintenance work have left almost half of the U.S. fleet of F-35 unable to fly on any given day. However, there is sufficient inventory of the fuel pipes and production capacity to boost stocks, according to people familiar with the situation.
Lockheed Martin has resumed flying planes coming off its production line in Fort Worth, Texas, and said in a statement that it is supporting the review and working with Pratt & Whitney to "limit disruption to the fleet."
United Technologies shares were down 0.4% on Thursday, while Lockheed Martin shares fell about 1.2%.
The grounding comes amid a debate over the reliability and safety of U.S. military aircraft. Defense Secretary Jim Mattis recently called for improvements to the fleet. Military officials have said the airfleet suffered from budget cuts in recent years that have been reversed.
The F-35 fleet was temporarily grounded in 2014 following a fuel tank fire on a jet preparing for takeoff. Pratt & Whitney paid for repairs and a design fix to resolve the issue.
The F-35B jet that crashed in South Carolina on Sept. 28 is a different model. The pilot ejected safely.
The F-35B has a single Pratt & Whitney engine and a lift fan made by Rolls-Royce Holdings PLC that allows it to take off and land vertically.
Britain's Ministry of Defense, which is conducting trials of the jet on an aircraft carrier off the U.S. East Coast, said Thursday that it was inspecting its planes as well. One plane resumed flying Wednesday after inspectors found the part under scrutiny wasn't in use on the jet.
The F-35, used by the U.S. Air Force and the Marine Corps, is also due to start flying from Navy aircraft carriers next year. Italy, the Netherlands, Israel and Norway are also flying the planes.
Israel, which used an F-35 in combat for the first time earlier this year, said it was inspecting its own fleet, though aircraft remained available for flying if required.
Lockheed Martin earlier this month secured a $11.5 billion deal for the next batch of F-35 jets, which included new incentives and penalties to improve its production performance after some planes were delivered late. The company had to freeze production for a time earlier this year because of a separate fuel-system problem.
--Robert Wall contributed to this article.
Write to Doug Cameron at email@example.com