A dual generator failure that caused the F-35 Joint Strike Fighter test fleet to be grounded on March 11 has been attributed to a faulty maintenance procedure which left excess oil in the aircraft’s lubrication system, according to the Joint Program Office (JPO).
According to reports maintenance documents have been now been changed to improve procedures, with newer F-35 test aircraft fitted with a newer engine/starter generator (AF-4, 6 and 7, BF-5 and CF-1) now cleared to return flying.
“Previous maintenance procedures could allow a small amount of extra oil to remain within the generator following servicing. Under some conditions, the extra oil that is churning inside a narrow air gap within the AES/G [alternate engine starter/generator] could cause internal temperatures to increase. It was assessed that high temperatures led to the generator failures,” a statement from the JPO noted.
Older test aircraft AF-1, 2 and 3, and BF-1, 2, 3 and 4 were fitted with an earlier type engine starter/generator and have not been affected, having previously been cleared for flight on March 14. The JPO has maintained that there will be “no significant impact to the System Development and Demonstration (SDD) program or production operations”.
“Flight test schedules are built with a margin for precautionary safety stand-downs. The F-35 test programs at Edwards AFB, Calif. and Naval Air Station Patuxent River, MD remain ahead of their monthly flight test schedules.”
Test aircraft F-35A AF-4 suffered a dual generator failure and oil leak as it was completing a flight test at Edwards Air Force Base on March 9, which led to the grounding.