Pratt & Whitney is inspecting an F135 test engine after it automatically shut down following a stall indication during ground testing for the short take-off and vertical landing variant of the Lockheed Martin F-35 Joint Strike Fighter.
The incident occurred on 30 August on a test stand at P&W's West Palm Beach, Florida facility, where the company is working towards initial flight release of the STOVL F135 to support the planned May 2008 first flight of the F-35B.
P&W says the F135 was "completing a control model validation qualification test in powered-lift mode...when it automatically powered down based on a stall indication".
F135 is being tested with representative F-35B lift-fan inlet
Powered-lift mode means the STOVL F135's lift system - shaft-driven lift fan, roll posts and three-bearing swivelling nozzle - were operating at the time.
Pre- and post-event data are being analysed to determine the cause, and the engine's condition is being assessed via boroscope and visual inspections, says P&W, adding: "We will determine next steps once the findings of the investigation are known."
The test anomaly is not expected to impact the JSF development schedule, says Dan Crowley, Lockheed Martin executive vice-president and F-35 programme general manager.
The first F-35B, aircraft BF-1, is in final assembly at Lockheed's Fort Worth, Texas plant. Its engine and lift fan are due to be delivered in late October, leading to a roll-out by year-end.
There was a testing incident earlier this year when the composite shaft broke during an over-aggressive stall of the lift fan, damaging the engine, but P&W quickly resumed STOVL testing.
The engine manufacturer says it has accumulated more than 8,400h of development ground-testing on F135s including more than 4,300h on STOVL engines.