Major assembly on the Boeing 787-10, which the manufacturer describes as a straightforward stretch of the 787-9, has started.

The 787-10, which will be the largest variant in the 787 family of aircraft, will be 18 ft. (5.5 m) longer than the 787-9. It is expected to achieve first flight in 2017. First delivery is scheduled for 2018 to United Airlines.

Boeing said Kawasaki Heavy Industries began installing the circular frames into the midforward section of the fuselage on March 14 in Japan, which the manufacturer noted was two weeks ahead of schedule.

“Beginning major assembly early underscores the commitment, discipline and performance of the entire Boeing and partner team worldwide,” Boeing Commercial Airplanes VP-787 airplane development Ken Sanger said in a statement.

All 787-10 final assembly will take place at Boeing’s North Charleston, South Carolina facility.

Boeing has 153 firm orders for the 787-10 from nine customers, comprising 13% of 787 orders. The order figure is down slightly, mainly owing to United switching 787-10 orders that had been slated for delivery in 2020 and beyond to five 787-9s and four 777-300ERs that will start delivering in 2017.