Dreamliner "bird test" prompts design tweak

Boeing acknowledged Friday that the horizontal tail section of the 787 Dreamliner had cracked slightly during a so-called "bird-strike" test, but described the incident as a routine part of developing the new jet.

The Dreamliner program is under intense scrutiny as Boeing prepares to build the first all-composite airliner, so every glitch — or potential glitch — makes analysts and investors skittish.

Spokeswoman Lori Gunter said the test was part of the development process and not a certification test, so the company's engineers strongly object to applying "the f-word," meaning failure.

"It wasn't a test you pass or fail. It was a test you learn from," she said.

In the November test, engineers fired an 8-pound gel pack — simulating a large bird — from a high-speed cannon, hitting the leading edge of the winglike section. The test helps assess what would happen to the tail section if the plane collided with a real bird in flight.

The outcome was "a very small crack that we just weren't comfortable with," Gunter said. The crack extended through a thin metal strip along the leading edge to the carbon-fiber reinforced composite plastic of the tail structure.

The test was conducted at Boeing's research center on Marginal Way by engineers from Boeing and from Alenia of Italy. Alenia will build the horizontal tail when production starts.

Gunter said the damage was within the acceptable tolerances for an airplane to continue to fly safely. "We met that standard," she said.

She said Boeing also evaluates how much it will cost an airline to repair any damage. That factor prompted changes that were "really driven by the economics of the situation rather than certification or safety requirements."

Engineers decided to thicken the metal edging strip and to add an extra ply of composite tape at that point on the tail.

The horizontal tail, like the rest of the 787 airframe, is largely made from carbon-fiber reinforced plastic. The structure is built up by applying layers of graphite tape soaked in resin; it is hardened by baking in a high-pressure oven.

Gunter said thickening the ply was "an easy fix" that involved no significant redesign of the structure.

The test was part of "the standard way we do development work," she said, and its outcome will not slow down certification nor affect the program schedule.

As Boeing and its worldwide partners prepare to build the first 787, the Dreamliner program is under intense scrutiny. Every glitch is news. A report of a glitch or a schedule delay can send Boeing's stock down.

The share price plunged more than 3 percent last week when a Wall Street analyst reported that Japanese suppliers had failed to finish their work on the first sections shipped for assembly to Charleston, S.C.

Boeing downplayed that report and similarly dismissed other recent worries:

• Certification of the huge Dreamlifter air freighters that must transport parts has been delayed several months. Boeing says the flight vibration problem at the root of that is already fixed and the Dreamlifter can make early deliveries without certification — so the schedule isn't affected.

• Engineers switched from a wireless in-flight movie and entertainment system to a more traditional wired version. Boeing says the alternative turns out to be lighter — so the schedule isn't affected and it will save weight, too.

Gunter said that in Boeing engineers' eyes, a test could "fail" only if its purpose was to certify a finalized design.

"You really can't fail a development test. The only reason you are doing the test is to drive the design decisions." Gunter said.

Boeing did not need to retest the tail subsequently, she said, "because the computer analysis and the results of that initial test were enough to tell us what the design needed to be."

However, a bird-strike test on the tail will be done later as part of Federal Aviation Administration certification.

That one — using a real bird carcass, not a gel pack — will be pass or fail.

Dominic Gates: 206-464-2963 or dgates@seattletimes.com