A Pratt & Whitney analysis has narrowed the likely cause of a turbine blade crack on the F135 in February to a fault in the casting process, says Bennett Croswell, president of the military engines division.

The analysis indicates that the Lockheed Martin F-35 engine blade cracked despite being made correctly according to the blueprint for making the part, Croswell says. That finding points to a flaw in the casting process itself.

"There may be features in the castings that are allowed by the blueprint, but now we've learned that those features we should not allow," Croswell says.

P&W can either change the process used to make the casting of the turbine blade or simply throw out any blade that shares similar features of the one that cracked.

"It may be as simple as culling those blades that have that feature," Croswell says.

P&W is finalising an analysis of which option would be most affordable, and that report will be submitted to the joint programme office at the end of June.

The 4.2mm (0.17in) crack led to a relatively brief fleetwide grounding of the F-35 after it was discovered on 19 February. The crack developed on a third-stage turbine blade of the AF-2 prototype, which was routinely operated in conditions beyond the flight envelope as part of the test programme.

Source: Flight International