Rolls-Royce (R-R) and Boeing are starting to replace gearboxes on nine Trent 1000 engines due to power undelivered 787s for All Nippon Airways after the Japanese operator was forced to ground its fleet because of a newly discovered defect.

The last of the five ANA-operated 787s that were impacted by the precautionary grounding will be returned to service “in the next few days,” says a R-R spokesman. The engine manufacturer says three aircraft are now either back, or set to resume operation. Modified gearboxes are also currently being installed on the engines powering the other two aircraft, he adds.

This is a more optimistic scenario than that painted by the airline, which earlier said only two aircraft had re-entered service and that replacement gearboxes on the remaining three would take “another few weeks to fix.” However, the airline adds that overall disruption has been minimized by the use of substitute aircraft and said only two domestic flights had to be canceled on July 23.

In all, 17 Trent 1000s are affected by the problem, which has been traced to a manufacturing flaw in the Hamilton Sundstrand-made transfer gearbox. “Hamilton Sundstrand changed the manufacturing process for some of the gears, and we identified that, through running of an endurance engine, [and] this caused unexpected corrosion. We started to examine it and saw it was to do with a modification in the manufacturing process,” the spokesman says.

The particular issue affected the crown gear assembly and was caused by a change in the chemical etching process used to make the part. The endurance engine, one of several units running alongside a “fleet leader” program engine to detect issues ahead of in-service discoveries, revealed the change could lead to pitting in the part and a reduced service life. Although the endurance engine did its job, the discovery is a blow to R-R, which until last week was describing the engine’s debut with ANA as “the best ever entry-into-service for a Trent engine with dispatch reliability [of] around 99.9%.”

Quick Resolution

“We are now working with Boeing to resolve the issue with the other nine engines, and we are working with Hamilton Sundstrand to resolve the issue as quickly as possible,” says R-R. The issue does not affect the alternate General Electric GEnx-1B engine on the 787, which uses a different accessory gearbox system. The R-R gear design is unusual in that it takes power from the intermediate pressure spool, rather than the more standard front of the high-pressure compressor. The move enabled the accessory gearbox, which is fitted with two variable frequency starter generators and one hydraulic pump to provide electrical and hydraulic power to the 787, to be more efficient­— particularly for shorter-haul Japanese domestic operations.

Boeing, meanwhile, says, “We don’t expect the timing of any deliveries to be affected by this. If there are any customers who may be affected within the year, we will work with them privately.”

R-R adds that the overall slowdown in the rate of 787 deliveries to ANA “is a separate issue” to the gearbox problem. The delivery rate issue is more concerned with the company’s slower-than-anticipated production ramp-up of Trent 1000 Package B standard engines, which replaced the earlier Package A version on the initial delivery aircraft, he adds.