General Electric expects to clinch certification for the upgraded 787 engine within weeks, and it is midway through initial flight tests of the improved sister GEnx-2B engine for the Boeing 747-8.

It has been a long road, but seven years after the first run of the GEnx-1B engine for the 787, and five years after the -2B was powered up for the first time, the engine maker is entering the home stretch in development of what it hopes will be two engines that are either at or above specification.

Boeing and GE originally planned to run the individual performance improvement package (PIP) tests sequentially, but just as with the development of the original engine standard, delays to the 787 program mean the two efforts are occurring virtually simultaneously. Flight tests of the upgraded -1B PIP II for the 787 are set to resume after a four-month hiatus caused by the grounding of the aircraft due to the battery failures.

Flight testing of the improved -2B PIP for the 747-8, leveraging upgrades made to the 787 engine, have been underway on GE's 747 flying testbed since February. GE is about to ship the third of four flight-test engines to Boeing as part of plans to evaluate the PIP standard on a 747-8 within the next few months.

The GEnx-1B PIP II package was designed to bring the performance of the engine up to the original fuel-burn specification following the discovery that the baseline version was around 3% adrift. However the performance of the initial PIP I package, which was certificated in August 2011 and targeted at closing the gap by 1.6%, has resulted in fuel burn that is better than expected on initial aircraft in service. With the PIP II, which resumed flight tests this month on Boeing's ZA005 development 787, GE is optimistic that overall aircraft-level performance will reach or exceed initial goals.

The PIP II package, which also included a higher rating of 78,000 lb. thrust for the stretched 787-9, includes an effective increase in fan diameter of 0.5 in., optimized outlet guide vanes, a higher-flow low-pressure compressor, improved high-pressure compressor aerodynamics and durability improvements in the high-pressure turbine and combustor. Certification, originally targeted for late in 2012, was delayed because of lack of suitably cold weather last year for icing tests. Flight tests did get underway on ZA005 but were suspended when all 787s were grounded three months ago.

Engine tests for PIP II are “all complete from our perspective,” says GEnx program general manager Chuck Nugent. “The testing reports are all done, and the certification board is scheduled to be here [for FAR 33 engine-certification approval] this month. We are working through the rest of the program timing. The engines are fitted right now and have already flown.” The interrupted test effort was expected to resume following the completion of a check flight by ZA005 on April 9. .

Flight tests of the -2 PIP are meanwhile “going extremely well,” says Nugent. “The 747 flying testbed is about two-thirds of the way through its flights, and we're seeing excellent results in terms of performance. We were expecting to get 1.6% improvement in fuel consumption and, based on test data, we're optimistic we will be at or better than that.”

To combat the original fuel-burn shortfall of more than 2%, GE designed an all-new low-pressure turbine, and added compressor, combustor and turbine improvements from the 787 engine's PIP II upgrade. Together with better-than-expected 1% fuel-burn improvement seen by initial 747-8 operators on the baseline engine, added to airframe improvements instituted by Boeing, Nugent says the -2 PIP will bring the aircraft up to or beyond specification.

“The flying testbed shall wrap up in the next couple of weeks and will culminate with Boeing pilot demonstration flights in which we will do operability and air starts,” says GEnx-2B program manager Tom Walker. The final round of certification work includes endurance testing of the low-pressure turbine (LPT). “We do have some stress tests and vibration-system testing, but the key one is the LPT. It's not a full 'block' test, [an endurance test required for all new engines], since the low-pressure turbine is the same technology as the PIP II, so it is not 100% new.” GE hopes for engine certification by mid-year, clearing the way for deliveries on 747-8s by year-end.