August 2012

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Breaking: Structural flaw halts production of Alenia 787 sections

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CenterFuse_560.jpgAlenia Aeronautica has halted production of two major 787 structural components due to wrinkles in the fuselage skin caused by manufacturing flaws in subcomponents of the one-piece composite barrel, according to a letter obtained by FlightBlogger.

The letter's subject: "SECTION 44 and 46 STOP WORK ORDER FOR BARREL" details a correspondence between Jay Campbell, sr. manager for supplier management for the 787 fuselage supply chain, James E. Simmons section 44/46 sr. engineering manager and Ciro Occipinti of Alenia Aeronautica in Naples, Italy.

The letter, signed and dated June 23 on Boeing letterhead, was sent the same day Boeing announced the latest delay in the program citing a need to reinforce the side of body structure.

Boeing and Alenia Aeronautica did not respond to multiple requests for comment. The status of production at Alenia's Grottaglie facility remains unknown at this hour.

This structural issue, sources say, appears entirely separate from the wing fix. Section 44 and 46 are two of the four major structural components that comprise the integrated center fuselage. Section 44, a bonnet section, sits directly on top of the center wing box (section 45/11) while section 46, a complete barrel, is joined to the aft part of the center wing box.

Campbell and Simmons explain the justification behind the production halt as "related to stringer edge steps" causing wrinkles in the skin of the fuselage that were larger than previously "demonstrated during the [preproduction verification] PPV on these components."

Stringer edge steps, as one veteran composite engineer explains, comprise the stacks of the composite fibers that make up the longitudinal structure that is cured and bonded to the skin of the fuselage barrels to give it its strength.

The letter goes on to detail the recommendations for the proper step height of each layer of composite fiber, plus or minus a given tolerance. The letter says that the guide for building fuselage stringers includes a note that says that step heights beyond a given a specified tolerance "will lead to significant degradation of the structure."

The tolerances and dimensions of the stringer were specifically outlined in the letter and are not included in this report due to the proprietary nature of the information.

However, the letter continues:

"Boeing engineering evaluations of the cross-sections provided by Alenia demonstrate that negative margins exist in the line 7-19, and line 20 and on, configurations for section 46. Line 5 and 6 are still under evaluation. While efforts are underway to refine that analysis, it is doubtful that the negative margins will be recovered, and that repair of at least line 7-29 will be required."

Of those 25 shipsets, four have been delivered to final assembly in Everett, Wash, eight are undergoing center fuselage integration at Global Aeronautica in Charleston, S.C. and the remaining 13 are in Grottaglie, Italy.

Each 787 barrel section contains 80 stringers that run the length of the fuselage. The letter did not detail what portion of the 80 would require repair.

The size of the edge steps on the stringers, the letter says, were increased first on "line 5 when Alenia began using the GFM stringer manufacturing cell at Grottaglie."

Line 5 refers to Airplane Five or ZA005, the first General Electric GEnx powered 787, that entered final assembly in January of this year. Sections 44 and 46 were delivered by Alenia for integration at Global Aeronautica in April 2008.

GFM is a company that does milling, cutting, routing and forging of various materials, including composites components.

During the manufacturing process, the composite stringers are fabricated in a clean room, loaded onto the preformed mold, or mandrel, then are wrapped in a preset amount of carbon fiber tape. After lay-up, which is done by a robotic wrapping machine, the mandrel is bagged and moved to the autoclave for high temperature curing.

Boeing's instructions in the letter to Alenia was to complete any carbon fiber placement currently underway, but not to begin any additional bonding or curing of barrels.

According to the letter, specifications were authored to control the height of the "edge step" as a result of what was learned during preproduction verification (PPV). The letter states that Alenia determined it "cannot comply with the requirement" and had requested "that the step height control provisions be eliminated." Boeing concluded that "based on the structural analysis...this is unacceptable" because the wrinkles "represent a risk of a major repair to every unit that is built without engineering coverage."

Boeing's conclusions on this structural analysis were conducted on two scrapped barrel sections identified as being from Airplane 15 section 46 and Airplane 20 section 44. "Sections cuts from the scrapped AP15 barrel show wrinkle geometry well in excess of those found during the PPV." Adding that the specification "does not allow wrinkles in the skin, and the existing effects-of-defects data does not sufficiently characterize the structural performance of wrinkles of this magnitude."

Boeing has yet to provide a revised schedule, known internally Z18, that dictates the 787 production and delivery schedule to suppliers and airline customers. The company has said a revised planning schedule will be available by the end of September.

This structural issue appears to not affect the first flight planning for ZA001 through ZA004, but it is yet unknown if delivery planning of the early production aircraft will be impacted while this issue is being resolved.

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