By Andrea Shalal RAF FAIRFORD England (Reuters) - The U.S. Navy on Friday maintained a grounding order for F-35 B-model and C-model fighter jets built by Lockheed Martin Corp, saying it was still not clear what caused a massive engine failure on an Air Force F-35 jet on June 23. "At this time, I do not have sufficient information to return the F-35B and F-35C fleet to flight," Vice Admiral David Dunaway, who heads the Navy's Air Systems Command, said in an update to a fleetwide grounding order issued by U.S. officials on July 3. Dunaway said in the document that he was committed to returning the F-35 fleet to flight as soon as possible, but there was "no discernible event that represents a root cause." In the incident last month, the Pratt & Whitney engine on an Air Force F-35 A-model jet broke apart and caught fire while a pilot was preparing to take off from Eglin Air Force Base in Florida air base. Until the grounding is lifted, the U.S. Marine Corps and Britain will not be able to ferry four F-35B aircraft to Britain for the fighter jet's planned international debut at two air shows there this month - the Royal International Air Tattoo, world's largest military air show that began Friday, and the Farnborough air show, which starts on Monday and runs through July 20.

NBA superstar LeBron James made an emotional return to the Cleveland Cavaliers, departing the Miami team where he became a world-famous champion to seek similar success with his hometown club. Four years after leaving the Cavaliers to chase his first NBA title with fellow stars Dwyane Wade and Chris Bosh in Miami, an unapologetic James said he wanted to bring the long-suffering sports fans of his home region a championship. James took a four-year deal worth $88 million with Cleveland over a five-year Miami offer worth $122 million and intends to finish his glittering career at the Cavaliers.