The first two operators of the Boeing 787-8 are seeing better-than-anticipated fuel burn, despite prior expectations of below-par performance as a result of data from predelivery flight tests.

The numbers, though based on early experience with a relatively small fleet on a variety of routes, are surprisingly positive given the early configuration of the airframes and engines. The operators have not yet incorporated all the planned weight and fuel burn improvements of follow-on production versions.

Four of the current active 787 fleet are from an early production block in which each is thought to be around 8,800 lb. over specification weight, while the remainder are lighter aircraft built from the block point change introduced from line No. 34.

Boeing, which is expected to comment officially on the 787’s in-service fuel burn numbers at the Farnborough air show next month, is in the midst of introducing weight reductions and other enhancements to compensate for what was expected to be a relatively significant shortfall in the planned 20% improvement over the 767.

Yet figures from launch airline All Nippon Airways (ANA) show fuel savings are up to 21% on long-range flights, while figures for the General Electric GEnx-1B-powered aircraft at Japan Airlines (JAL) indicate potentially slightly better numbers.

GE says initial performance data show its GEnx-1B engine has a 2% fuel burn advantage over the competing Rolls-Royce Trent 1000, not counting an additional 1% benefit from expected performance retention in terms of sustained exhaust gas temperature margin. The first GEnx-1Bs are in service with JAL, while 787 launch operator ANA uses aircraft powered by the Trent 1000.

ANA earlier this month was the first to reveal that its aircraft were producing around 21% lower fuel burn on international flights compared to the 767-300ER that the 787 is designed to replace.

The airline, which accepted its ninth aircraft on June 24, is believed to have been anticipating a 17-19% improvement, based on the Trent 1000 Package B that Rolls introduced to counter some deficiencies seen in flight testing.

After its first six months of service, ANA says the 787 efficiency levels are slightly up on the 20% savings originally expected at the beginning of the program. On domestic routes, the saving is 15-20%, which meets expectations, say ANA officials. The short-haul sub-fleet includes four early delivery aircraft powered by the interim Trent 1000 Package A standard engine. ANA’s long-haul configured 787s operate between Tokyo Haneda Airport and Frankfurt Airport, with additional transpacific routes from Tokyo Narita International Airport to Seattle-Tacoma International Airport and Norman Y. Mineta San Jose International Airport in California due to be launched by early 2013.