While the installation of the 787 wing fix continues, Boeing engineers have returned to the drawing board to redesign part of the reinforcement, FlightBlogger has learned.
As a result, company and industry sources say the 2009 first flight target could be in jeopardy as engineers work to redesign the fix for four remaining wing stringers.
Boeing declined to discuss the modifications, saying that the next opportunity for an update will come on October 21st during the company's third quarter earnings call. However, the company did reaffirm that 787 "will fly by the end of the year."
Internal schedules, say several program sources, initially targeted October 15th for ZA001's to return to ground operations with a first flight to follow roughly six weeks later, however the aircraft remains in the paint hangar as engineers work to complete the design and installation of the side-of-body reinforcement.
The structures in question are stringers 2 through 5, the shortest and highest load stringers positioned in the aft of the wing boxes. Each wing box has 17 stringers designated 2-18.
Program sources indicate that the initial fix design for stringers 2-5 did not meet certification margins in computer modeling.
FAA certification requirements dictate that the wing must withstand 150% of the maximum load the aircraft will ever encounter in service. Industry and company sources say that the wing withstood around 105% before the stringer delamination was encountered in static testing, however Boeing has never publicly disclosed the number.
One source familiar with the wing fix says that the solution will remain consistent with what Boeing originally envisioned, but adds that the reinforcements could vary in length and/or location.
In a message to program staff on October 12th, 787 vice-president and general manager, Scott Fancher indicated that the progress on the installation is paced by engineering development.
Fancher said, "we are making headway on the [side-of-body] modifications. Great progress being made on engineering releases by the design team. This allows us to continue with the installation of fittings on the initial airplanes. The pace of the modification is increasing and I am confident that this integrated team will lead the way to first flight"
The company is working day and night to install the modification deep inside the center wingbox and wing structure of the 787 test fleet.
Sources add that installation of the existing design is progressing well, with ZA002 and ZA004 rapidly catching up to ZA001 and ZY997 as the learning curve for the installation has already begun come down.
Once the installation is complete ZY997, the static test airframe will undergo full-scale testing of the reinforcement that Boeing hopes will validate the design, clearing the way for the 787 to fly.