Boeing expects to start delivering improved 787 Dreamliners in first half

Improvements to the maximum takeoff weight of the wide-body planes will let airlines fly a further 400 miles (643 km) or five to six tons of additional cargo, said Darren Hulst, Boeing's vice president of commercial marketing.

"Those aircraft are actually already in the production system, moving through towards certification, and we anticipate deliveries of those aircraft beginning the first half of this year," he told reporters on the sidelines of the Singapore Airshow.

Hulst also said the planemaker expected the larger 777X to be certified in the second half of the year, though it might not enter service until next year.

"When we think about the difference between certification and entry into service, it's really up to our customers when they take delivery of the aircraft and the processes and steps they need to go through between certification and ultimately revenue service for that aircraft," he said.

Reuters reported on Tuesday that Boeing planned the first flight of a production 777X in April, in an important sign of progress for its long-delayed new jet.