Final flight tests of GE Aviation’s GE9X turbofan engine have been completed on the company’s Boeing 747-400 flying testbed ahead of the engine’s first flight this summer on the 777-9, the initial version of the US aircraft manufacturer’s new 777X twinjet series. The flight test campaign, which began in December 2018, stretched over more than 50 flights and 320 flight hrs., and followed an earlier preliminary test program between March and May 2018.