Key 787 crash test today

Boeing is set to perform a crash test today on its 787 Dreamliner — by dropping a section of the fuselage from the height of a second-story window.

Boeing has not done crash tests to get previous jets certified to fly. It's necessary this time because the 787 is the first airliner built largely out of carbon-fiber-reinforced plastic, which is more brittle and less shock-absorbent than metal.

The procedure, which federal aviation regulators will monitor, may not seem like much of a trial for a jet that will travel 550 mph at 35,000 feet.

But the test isn't designed to simulate a full-tilt fall to Earth. Rather, it replicates the vertical impact of an emergency landing in which the plane hits the ground harder than normal — often referred to as a crash landing.

While typically no one aboard survives a catastrophic, out-of-control airplane crash, a modern airliner should allow passengers to walk away from a heavy emergency landing on essentially flat terrain.

The Federal Aviation Administration mandated in June that before the 787 enters service, Boeing must prove that passengers would have at least as good of a chance to survive a crash landing as those aboard a traditional aluminum airframe.

"We have a high degree of confidence," said Jeff Hawk, Boeing's 787 executive responsible for certification, who will watch the test at Boeing's Apache helicopter manufacturing facility in Mesa, Ariz.

Observed by FAA technical specialists, Boeing engineers will drop a 10-foot-long fuselage piece from a height of about 15 feet onto a 1-inch-thick steel plate. It will hit the ground at around 30 feet per second.

No crash-test dummies will be aboard the test fuselage, unlike two vertical-drop crash tests conducted in 1999 and 2000 by the FAA and NASA on two 737 fuselage sections. Those tests were conducted to explore specific interior configurations, not as part of 737 certification.

Instruments will be positioned in the seats, with ballast to represent passenger weight.

High-speed cameras, strain gauges and accelerometers will minutely record the impact's effect, including the force that would be exerted at the base of a passenger's spine.

The fuselage section being used is not a complete barrel. Its top was removed to make it easier to lift and drop, and engineers attached crosstie beams at the top to keep it as rigid as the original.

Boeing will not release detailed test results, which are considered proprietary.

In any case, the outcome is not pass/fail. The test is designed to discover whether the real airframe performs as Boeing's sophisticated software modeling tool predicts.

Based on previous tests, Hawk believes it will.

Boeing must then spend months simulating other crash scenarios on superfast computers — with the plane hitting the ground at different speeds and various angles.

The outcomes of those simulations, comparing the 787 results with metal jets in similar crashes, will be presented to satisfy the FAA's requirements and win certification before the plane is due to enter service in May.

Today's vertical drop will be Boeing's third and final crash test on the Dreamliner.

The first test at Mesa involved crushing a fuselage section slowly between steel plates, "like a great big vertical vise," said Hawk.

"Essentially, in a very slow time-frame and in a controlled test environment, we can see where the various pieces buckle and bend," he said.

In the second test, performed a few months ago, a steel plate was suspended above and then rammed into a fuselage section positioned upside down on the ground.

"Essentially, we brought the runway to the airplane," said Hawk. "When you talk crush characteristics, it doesn't matter if the ground is coming at you or you are coming at the ground.

"That test was deemed very satisfactory," Hawk added. The results matched the mathematical model.

Ed Fasanella, a senior NASA engineer and crash expert, worked on the two earlier 737 drop tests and is involved with extensive crash testing at NASA's Langley Research Center in Virginia.

Fasanella said that in a crash landing, the forward momentum is usually not a problem because the plane skids along for some distance. It's the instant deceleration in the vertical dimension, with a hard stop at the ground, that can cause injury or death.

He said that if a plane hits the ground at a vertical sink speed of 42 feet per second or faster, there likely won't be survivors.

That's why a vertical drop test is key to the analysis.

"Since it is composite, it's harder to analyze," Fasanella said, "You almost have to do a physical test."

While metal bends and crumples rather than breaking under high loads, he said, carbon-fiber plastic composites are typically "brittle."

So engineers must design a composite airplane with that in mind.

"If you do it in certain ways, you can make it similar to metal," Fasanella said. "You have to be careful with attachments. It's better to bond instead of drilling holes and bolting."

Boeing's Hawk said the manufacturer has been doing exactly that: "tailoring the airframe structure" using the predictions of the crash analysis software and refining the design "so that we have an energy-absorbing structure."

In the plane's subfloor, the most crucial area for protecting passengers, engineers modified the thickness of the cargo-floor composite supports.

These supports are also set at a slight angle as part of the basic design, so that the subfloor structure will crumple in a severe impact to absorb some of the shock, Hawk said.

Because the previous tests went so well, Hawk said it "would be a tremendously unexpected surprise" if the results of today's drop test are different from predicted.

Boeing's first response in that case, Hawk said, would be to look into a retest, on the assumption that measurement instruments might have failed.

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