Boeing later today is expected to conduct initial taxi tests of the 787-9, following completion of a full series of final pre-flight ‘gauntlet’ ground simulation tests in Everett, Wash., and could conduct first flight as soon as tomorrow.

“We have successfully completed a number of key lead-up milestones in recent weeks. We’re on track for first flight in the coming days, as early as Tuesday, Sept. 17,” the manufacturer says.

Test engineers this weekend were evaluating the avionics, primary flight control system, engines and other systems on ZB001, the first aircraft, in preparation of high-speed taxi tests. The initial gauntlet tests began around Sept. 10.

While last minute system or test issues could delay first flight later into the week, the weather also may play a factor in the precise timing of the attempt. The forecast for Everett indicates light and variable winds early on for Sept. 17, with winds picking up later in the day. Although a weather system passed through the area yesterday, the unsettled conditions it left in its wake are not expected to result in significant rain on Tuesday.

While rain itself is not a major factor for a first flight, low-level cloud and winds are more serious considerations.

Testing also is underway on the second assembled 787-9, ZB002, which is expected to join the flight-test program sometime in October.

The 787-9 certification effort is due to be completed in the second quarter of 2014 ahead of the first delivery to launch customer Air New Zealand around the middle of the year.

As well as three development aircraft, the test program will include two aircraft with fully configured passenger interiors that will undertake pre-entry-into-service function and reliability work. One of these aircraft, line number 146, is scheduled for eventual delivery to All Nippon Airways, which has 30 787-9s on firm order.

The final gauntlet tests—which precede the taxi-tests—will run the systems in a closed-loop simulation of the first flight. The testing is expected to be divided into two primary blocks with the first simulating a typical ‘B1’ first flight profile, the standard checkout of a normal production aircraft, and the second block a more rigorous “first flight” simulation of a test and failure scenarios.