Boeing today successfully completed the first flight of its 787-9, the airframer’s initial stretched derivative of the company’s 787 twinjet series.

The test flight started just after 11 am when the aircraft took off from Boeing’s facility at Everett, Wash. and ended 5 hr. and 15 min. later at 4:18 pm when it touched down at Boeing Field in Seattle.

The flight included a standard “B-1” Boeing production test flight, as well as flight testing related to specific differences associated with the propulsion system and handling characteristics of the longer airframe. The aircraft, designated ZB001, is 20-ft. longer than the baseline 787-8, and is powered by the newly-certificated ‘Package C’ version of the Rolls-Royce Trent 1000.

The test debut of the 787-9 marks a major milestone for the program, as Boeing continues to ramp up deliveries of the 787-8 and start development of the 787-10, the third major derivative of the family.

Boeing has high hopes for the -9 stretch, particularly since the higher capacity variant does not trade performance for the additional 40 passengers it will hold compared to the -8.

The aircraft is designed to fly an additional 300 nm with a full payload compared to the baseline, and has already attracted firm orders for 388 units. This represents 41.5% of the company’s overall 787 firm backlog, a figure comparatively close to the 787-8’s current 498 order tally.

Boeing also appears more confident about meeting initial performance goals with the 787-9 than it did with the troubled early development versions of the 787-8. This is largely because the 787-9 empty weight is reportedly running marginally better than predicted.

The aircraft also incorporates aerodynamic improvements including a hybrid laminar flow control device in the vertical fin and will benefit from the latest fuel burn improvement packages developed by Rolls for the Trent 1000 and General Electric with the PIP II package for the GEnx-1B.

The Package C engines powering the aircraft on its first flight are rated at 74,000-lb. thrust, and designed to have 1% better fuel burn relative to Package B. The upgraded configuration incorporates modifications to increase mass flow and exhaust gas temperature margin, and includes modified blades in the intermediate pressure compressor and a semi-active case cooling system for improved tip clearance control in the low-pressure turbine.

The engine will be the baseline engine for the 787-9 when it enters service with Air New Zealand in mid-2014, and also will power 787-8s from around June 2014 onwards.

The first test aircraft will be based at Boeing Field for the majority of the upcoming test and certification campaign, which will be completed in the second quarter of 2014.

ZB001 is the 126th 787 to roll off the Boeing’s Everett and Charleston, S.C, production lines, and will be joined in the test program by the second and third 787-9s, ZB002 and ZB021. The second test aircraft has been completed and the third is in final assembly.

Two 787-9s with completed interiors will also join the latter stages of the program to assist with function and reliability pre-entry-into-service tests.

[Editor’s note: this article is updated to reflect the completion of the first flight]