Boeing Says Development Test Not Part Of Certification Program

Acknowledging that its 787 Dreamliner sustained a crack in the horizontal tail section during a recent bird strike test, Boeing spokespeople were quick to rally around its newest aircraft project, contending that the episode was just a standard event in the development of a new aircraft. 

According to Boeing spokeswoman Lori Gunter, the test was part of the development process and not, she said, a certification test. Company engineers, she added, strongly object to applying "failure" to the results.

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

In Boeing engineers' eyes, she said, 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's Dreamliner program is under intense scrutiny, according to the Seattle Times, so every hiccup -- or potential problem -- is quick to have an effect on analysts and investors.

Although bird strike testing by manufacturers originally involved firing a bird carcass from a gas cannon into the test unit, the carcass was soon replace with suitable density blocks, often gelatin. Testing is also done with computer simulation, although final testing often involves physical experiments.

To test how an in-flight bird collision would impact the tail section, engineers fired an eight-pound gel pack from a high-speed cannon at the leading edge of the wing like section. The November test was conducted at Boeing's Seattle research center by Boeing and Alenia, Italy, engineers. Alenia is building the horizontal tail when production begins.

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

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

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

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

Thickening the ply was "an easy fix," she said, that involved no significant redesign of the structure.

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

The test was part of "the standard way we do development work," Gunter said, and its outcome will neither slow certification nor affect program schedule.

A bird-strike test on the tail, using a real bird carcass, will be conducted later as part of Federal Aviation Administration certification.

FMI: www.boeing.com