The problem-plagued F-35 JSF program has been dealt another setback with an in-flight failure of the power generator and an oil leak on the same aircraft during the flight. The pilot of the aircraft dubbed AF-4 was able to safely land the aircraft.

Reuters reports that the entire fleet of ten F-35 aircraft has been grounded pending an investigation into what caused the leak and power generator failure during the test flight. The aircraft was flying out of Edwards Air Force Base in southern California at the time of the incident according to Lockheed spokesman John Kent.

Reuters reports that the F-35 fleet was grounded as a routine precaution. Kent said, "Once the cause is known, the appropriate repairs and improvements will be made before flight operations resume."

Flightglobal.com reports that this is the second grounding of the F-35 fleet in only six months. The last grounding of the fleet was due to a software issue that was discovered in simulations. The glitch could have forced the fuel pump to shut down at altitudes in excess of 10,000 feet.

This is the first in-flight problem with the conventional take off and landing version of the F-35 that will be flown by the Air Force. 

The generator has been an issue with the carrier-based version of the F-35 in the past with the acknowledgement in 2007 by Lockheed that the generator was sized to provide only 65% of the power requirement of the F-35C. The first production F-35C had its maiden flight in February.

Other systems of the F-35 have also had problems. One of the most notable is the F-35 helmet that has issues with video feeds lagging among other things.