Wall Street Journal: Dreamliner Woes

06/24/09

Attorney, pilot and aviation engineer Mike Slack comments on Boeing’s disclosure of design troubles with its 787 Dreamliner.

Dreamliner Woes Point to Difficulty of Using High-Tech Materials
By Andy Pasztor and Peter Sanders, The Wall Street Journal
Published June 24, 2009

Despite the steadily increased use of carbon-fiber composite parts in airlines, Boeing Co.’s disclosure Tuesday of design troubles with its 787 Dreamliner highlights the engineering, manufacturing and maintenance issues still associated with such high-tech materials.

By indicating that “a relatively small number” of added internal structural supports are needed on some of the upper portions of both wings, the disclosure underscored a broader problem that the aerospace industry has recognized for a while: shortcomings in computer-design systems’ abilities to precisely predict behavior of certain composite parts as they bend and twist in flight.

The areas of the 787 under scrutiny involve a blend of metal and nonmetallic composite materials. Independent structural experts said Tuesday that even the most advanced computer-models sometimes have difficulty accurately predicting how stress will affect the composite parts, or where they attach to aluminum or titanium. In such circumstances, “stress paths” within or between components can be unpredictable.

Regularly scheduled stress tests on the ground revealed that portions of the airframe – specifically some areas where the top of the wings join the fuselage – experienced greater strain that computer models had predicted. According to some Wall Street analysts and independent structural experts, it could take months for Boeing to implement a design fix, run more ground tests and adjust computer models to better reflect real-world conditions. The nature of the latest delay also raises the possibility that other portions of the predictive computer models could turn out to need further verification and perhaps adjustment.

Both Boeing and European rival Airbus have opted to reduce weight by relying on composites in their latest jetliners. The trend generally has been successful and has been embraced by airline customers. In announcing the fixes and related test-flight delays, Scott Carson, chief executive of Boeing’s Commercial Airplanes unit, made a point of saying that the moves aren’t “related to our choice of materials or the assembly and installation work” on the 787 Dreamliners.

Still, some outsiders were surprised by the company’s timing. “This is pretty late in the game to get a surprise of this type,” said Mike Slack, an aviation-accident attorney and structural expert who previously worked on structural and composite issues affecting the U.S. space shuttle program. “The analytical phase should have provided an understanding of the stresses and stress paths.”

Other jetliners have encountered high-profile structural problems late in their development. In early 2006, the Airbus A380 “superjumbo” failed a stress-test of its wings as the two-deck plane was in flight tests and just months before it was slated for certification and first delivery. Airbus later reinforced the wings, but the issue became less urgent as other, more serious manufacturing missteps delayed the aircraft.

Boeing’s stumble is striking because in the past, concerns with high-tech composites generally have focused on the manufacturing challenges of turning out ever-larger composite parts with extremely tight tolerances.

Maintenance also has cropped up as a major issue since the early part of the decade. Boeing for years has worked to perfect 787 repair kits – complete with portable vacuum packs – to help mechanics quickly repair cracks or dents as they are discovered.

This month, the Federal Aviation Administration asked for public comment on proposals to update aircraft-certification rules to better take into account widespread use of composites. Adoption of such materials “requires additional or modified standards to maintain the level of safety currently required for metallic materials,” according to the agency.

Several weeks ago, the FAA issued a rule requiring X-ray and ultrasound inspections to look for damage to certain parts of carbon fiber-reinforced plastic rudders on Airbus A330 and A340 wide-body aircraft.

In early 2006, U.S. and Canadian aviation-safety watchdogs also urged Airbus to devise enhanced inspection techniques to check the structural integrity of rudders on more than 370 of the manufacturer’s A300 jets. U.S. regulators followed up with mandatory requirements for more-extensive inspection and maintenance procedures.

Debate about the need to go beyond visual inspections sparked public attention after a March 2005 incident in which the rudder of an A300 flown by Canadian airline Air Transat ripped off in midair. The pilots managed to land the aircraft safely. But subsequent inspections revealed that leakage or fluid inside certain composite parts on some Airbus models could damage rudders by undoing the internal bonds between carbon fibers.

– Daniel Michaels contributed to this article.

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