F135 Blade Failure Could Hold Up STOVL JSF

By Guy Norris

First flight of the first short take-off and landing (STOVL) Lockheed Martin F-35 Joint Strike Fighter, BF-1, could be delayed following a repeat of the Pratt & Whitney F135 engine turbine blade failure that led to a hold up in flight tests last year of the conventional take-off and landing (CTOL) JSF.

The failure of the low pressure (LP) turbine blade is thought to have occurred in engine six which was undergoing flight clearance "proof test" ground runs prior to installation in the first STOVL F-35, BF-1. The tests were aimed at proving, on an engine-by-engine basis, that the specific unit was safe to use in BF-1, and that it did not exhibit the same combination of assembly characteristics, tolerances and other factors that led to a similar failure on a test stand engine on August 30.

The August failure, which contributed to a prolonged delay for both ground and flight tests of AA-1, the first conventional flight test F-35A, was traced to an unsteady flow regime in the wake of the stator upstream of the LP turbine third stage. P&W is developing a fix involving redesigning the stators and is planning to test the improved configuration by the middle of this year. In the meantime it cleared specific engines to allow flight test to resume of AA-1 in December 2007, and hoped tests of engine six would similarly clear the way for BF-1 to start tethered hover pit tests originally set for April.