Boeing's 787 customers are urgently waiting to hear when they can expect to see their first Dreamliners after the programme suffered another major delay. The latest interruption is due to the need for structural reinforcement to the wing/body attachment structure.
Just days shy of the latest first-flight target, Boeing postponed that illusive milestone after static testing in late May revealed a defect that would have greatly limited the flight envelope required for productive flight testing.
"Preliminary analysis was that we could have a credible flight-test envelope, but then during detailed analysis the envelope narrowed to the point that it would not be useful for flight-test," says Boeing Commercial Airplanes chief executive Scott Carson.
How the latest 787 delay unfolded
- 20 March The 1g static test is conducted on 787 static test airframe (ZY997), flexing the wings to checking for interferences in the control surfaces.
- 21 April 120-130% of limit load applied to wings, resulting in a deflection of over 5.2m (17ft). The test marked the completion of the pre-flight static testing required ahead of first flight.
- Late May Further wing deflection tests undertaken and structural strain gauge readings observed that are inconsistent with model expectations, with damage on the upper part of the wing-to-body join. Further tests carried out to assess the impact of the results.
- 14-15 June Boeing Commercial Airplanes chief executive Scott Carson and vice-president of airplane programmes Pat Shanahan reaffirm at the Paris air show that 787 prototype (ZA001) remains on schedule to fly by the end of June.
- 19 June After detailed analysis of the wing-to-body join, Boeing determines the flight envelope is prohibitively small and the company decides to postpone first flight.
- 23 June First flight postponement is announced due to the need for structural reinforcement, with revised flight-test and delivery schedule to be available "within the next several weeks".
With the airframer yet to even finalise what remedial action is required, Carson will not put an estimate on how long the issue will delay flight-testing, saying only that a revised schedule for the first flight and service entry will come in "the next several weeks".
However, with the need to go back into the detailed design phase for the fix, combined with the need to fabricate, install and test at component and full-scale levels, several sources close to the situation estimate that the fix will take "months, not weeks".
The first 787 was due for delivery in the first quarter of 2010 to Japan's All Nippon Airways, a date that is almost certainly going to slip again because of the knock-on effect of the flight-test delay, says Carson.
"We are disappointed that the first flight will be postponed, and urge Boeing to specify the schedule for the programme as a whole as quickly as possible," says ANA.
Even though its 787 test fleet will remain grounded until the fix is installed, Boeing will proceed with the final gauntlet and low-speed taxi tests to continue to mature the aircraft systems ahead of the formal start of the flight-test programme.
The fix, once identified, will be able to be installed on the aircraft in the factory, the flight line and at supplier partners without any anticipated schedule disruption.
"The area in question is a few square inches in the side of body," says Scott Fancher, vice-president and general manager of the 787 programme. "The modifications are relatively small without very much weight [penalty] and a negligible impact on performance."
Sources directly familiar with the issue say the area requiring reinforcement centres around the upper wing-to-body join that mates the wing box (Section 12) from Mitsubishi Heavy Industries and the centre wing box (Section 11) from by Fuji Heavy Industries. The area of concern centres on the 18 points where Sections 11 and 12 meet.
More specifically, the 18 points on each side of the aircraft (36 in total) are located on the top panel of the centre wing box and run port to starboard inside the structure of the centre wing box. These 18 stringers inside the centre wing box are matched by 17 stringers on the wing box, which serve to stiffen the wing skin. The wing box has 17 stringers, but a source indicates they are designated 2-18, hence the reference to the 18 points that require reinforcement.
The composite stringers, which give the wings its longitudinal stiffness, are cured during production when cooked in the autoclave and joined as a single bonded piece with the wingskins.
On the inboard side of the wing box where the 17 stringers end and connect to the centre wing box, each has what is known as a "stringer cap" that widens at the end and actually makes the hard connection between Section 11 and Section 12 on the side of body. The stringer caps on the static airframe, ZY997, sustained damage, albeit repairable, when the wings were flexed in late May.
Boeing confirms that small areas of the wing structure separated or "disbonded" from the wing skin, but declines to specify exactly where. Sources directly familiar with the situation say the shifting tension load from the stringer to fastener head also caused damage on the structure.