Pratt & Whitney’s F135 fighter engine that powers the Lockheed Martin F-35 is the target of two new US government reports criticising the propulsion system’s “very poor” reliability and 61 nonconformities with P&W’s own and the Department of Defense’s (DOD) quality management procedures.

The findings by the US Government Accountability Office (GAO) and the DOD Inspector General appear less than two months before the US Marine Corps prepares to declare initial operational capability with the first F-35B squadron.

But Pratt & Whitney argues that the GAO is mischaracterizing the F135’s reliability data and the IG report’s findings about the company’s management system do not reflect the quality of the end-product.

“The engine is reliable, and we’ll continue trying to make it more reliable,” Bennett Croswell, president of P&W’s military engines business, told reporters on 27 April.

The GAO reported on 14 April, however, that a key reliability metric for the F135 – the mean flight hours between component failures – is tracking well behind a planned growth curve.

At this point in development, that curve suggests the conventional take-off and landing version of the engine should operate more than 100 flight hours between failures, the GAO says. Fleet data shows the fleet averages a failure roughly every 25h. The short take-off and vertical landing version of the engine should be averaging about 90 flight hours between failures, but averages closer to 45, the GAO says.

Croswell acknowledges the accuracy of the GAO’s numbers, but says that report does not reflect the overall picture of the F135’s reliability record.

Although mean flight hours between component failures is below expectations, two other key reliability metrics – mean flight hours between removals and full mission capability rate – is running above expected levels, Croswell says.

Moreover, P&W’s ground-based testing of the production configuration shows that version should meet current reliability targets once it enters flight operations later this year, Croswell says.

Although the IG was sharply critical of P&W’s quality management system, Croswell says the company stands by a commercially-derived programme that it has adapted for the F135.