The US Department of Defense (DoD) has ordered mandatory inspections of all three variants of F-35 Lightning II joint strike fighter (JSF) before the jets resume flying operations.
The order comes after a US Marine Corps' F-35B short take-off and vertical landing (STOVL) variant suffered an in-flight emergency due to an engine oil problem last week at Marine Corps Air Station Yuma in Arizona, US, prompting Pentagon to temporarily ground the entire fleet.
F-35 programme office spokesman Joe DellaVedova was quoted by Reuters as saying that the inspections had been ordered on 13 June, and a large number of planes had completed inspections and had been cleared to resume flights today.
The inspections were primarily focused on the oil flow management valve fitting on all F135 powerplants that provides oil flow to the engine bearing compartments, DellaVedova added.
Commenting on the F-35B incident, DellaVedova said issues have now been found with a total of three valves, while noting that the engine oil leak source appeared to be a supply line to engine bearings and a fitting that separated from the body of the valve in question.
No issues have been discovered in F-35s flown at the other bases in California, Florida, Arizona and Maryland, DellaVedova said.
Meanwhile, F135 engine manufacturer, Pratt & Whitney spokesman Matthew Bates said the company is closely working with the F-35 programme office to determine the root cause of the issue.
Inspection on each aircraft lasted for around 90 minutes, and nearly all planes had been inspected and cleared for further flights, Bates added.
A derivative of F119-PW-100 engine, the F135 is an afterburning two-shaft engine, and is claimed to have completed 32,000 hours of combined ground and flight testing, including more than 16,000 hours of operational flight, as reported by Agence France Presse.
Built by Lockheed Martin, the F-35 JSF is a fifth-generation multi-role fighter aircraft designed to conduct an array of ground attack, reconnaissance and air defence missions with stealth capability.
Image: The Pentagon temporarily grounded its entire F-JSF fleet at following an oil leak involving the F-135 engine. Photo: courtesy of Duch.seb.