Investigators have narrowed their focus to the third stage turbine of the F135 engine as the likely source of a fire that erupted June 23 as an F-35A fighter was preparing for takeoff at Eglin AFB, Florida, last month.
The third stage turbine is the second stage in the low-pressure turbine section. It is common to all F135 variants – the A, B and C F-35 aircraft.
In addition to the flight grounding, "We cannot run any engines," including those in testing at the contractor’s facility, as a result of the fire, U.S. Air Force Lt. Gen. Christopher Bogdan told Aviation Week during a July 3 interview.
http://aviationweek.com
Unfortunately there was a possibly related issue in 2013.
21-February-2013, the Pentagon ordered a grounding for all F-35 aircraft, after a routine check at the Edwards Air Force Base revealed a crack in a low pressure turbine blade in an engines of a F-35A.
It was a F-135 engine with 700 hours, of which 409 flight hours. The aircraft was the F-35A test aircraft AF-2. The half-inch long crack was found in a turbine blade of the low pressure turbine section. This makes it unlikely that it is caused by so-called FOD (Foreign Object Damage), such as a bird strike, because such an object has to pass the Fan Section (3 stages) Compressor Section (6 stages), combustor and high pressure turbine section before reaching the low pressure turbine section.
JSF Nieuws.nl » F-35 fleet grounded after new F-135 engine problems