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Testing Data Recorder Improvements

UDRI Simulates Aircraft Crash Impacts to Determine Whether "Black Box" Data Will Survive

What gets shot from a cannon at 350 miles per hour, comes to a dead stop in 18 inches within 6.5 milliseconds -- and survives?

A memory unit destined to record data inside a "black box," the common name for the flight data recorder and cockpit voice recorder inside business, commercial and military aircraft.

Engineers in the University of Dayton Research Institute routinely shoot new and improved memory units out of a 40-foot gun and into an aluminum honeycomb barrier in the Impact Physics Laboratory so black box manufacturers can determine whether data stored on the unit survived an impact simulating an aircraft crashing into the ground.

"Black box manufacturers don't care if the unit's housing or the electronics don't survive a crash," said Kevin Poormon, a UDRI mechanical engineer who designs, conducts and monitors the impact shock tests. "Only the memory unit inside has to survive."

After an aircraft accident, investigators open the black boxes and download data from the crash-survivable memory units, or CSMUs, to reconstruct the event and determine what went wrong so steps can be taken to make planes safer. Aircraft passengers have black boxes to thank for such safety advances as ground-proximity warning systems, which alert pilots to fast-approaching terrain.

UDRI is one of only two organizations in North America that conducts impact shock tests for the Sarasota, Fla.-based Aviation Recorders division of L-3 Communications. Improvements often make the units more lightweight -- most today weigh less than 10 pounds -- or less expensive. "In the past, we were building crash-survivable modules out of stainless steel, and now we're building some out of titanium, which has less weight," said Mary Gayle Wright, communication manager for L-3's Aviation Recorders division.

Engineering redesigns, improvements or regulatory changes warrant impact shock tests, among others, to ensure any revamped CSMU receives Federal Aviation Administration approval. For example, some of L-3's units, which used to be square, are now cylindrical, which not only reduces their weight but also allows memory chips to be stacked and mounted more efficiently in the module.

The newest recorders have no moving parts, rely on computer memory chips rather than tape driven devices and record more flight data parameters -- as many as 300 -- for a longer time. Future units will likely record video images, and some may combine flight and cockpit voice data inside the same box.

"Any new model we submit must have FAA approval, so it has to go through the complete sequence of testing," Wright said. Memory modules must resist penetration, withstand crushing impact forces, and survive in spite of fire, deep sea pressure and immersion in water or other fluids. New or improved units must pass the impact shock test first -- or it's back to the drawing board.

"Sometimes we test the whole black box, and sometimes we just test the memory unit itself," Poormon said. "Every test we do is different."

Poormon designs each test based on the size, shape and weight of the test unit, which must be subjected to a peak impact that's 3,400 times the force of gravity -- 3,400 g -- for 6.5 milliseconds.

"The trick is to get the duration as well as the g profile," he said. "We get the duration we need by physically shaping the stack of aluminum honeycomb. We have to select the honeycomb cell size, foil thickness and material properties to get us in the right ballpark for the profile we need."

Once test parameters are designed, Poormon bolts the test unit inside a thick-walled can, called a sabot, which is shot from the 12-inch-diameter, 40-foot-long gun using compressed gas and crashed into the stacked aluminum honeycomb barrier.

The launch package crushes the honeycomb as it decelerates to a stop.

"The test is designed to be more severe than the unit would experience during a crash event," Poormon said. "That's because black boxes have to survive, even if everything else doesn't survive."

As long as Poormon has achieved the required profile, the impact shock test -- from his perspective -- is a success. What he doesn't know is whether the data inside the unit survived the impact; that's for the manufacturer to determine. After the test, Poormon ships the test unit, high-speed films of the test and a test report with computed shock data back to the manufacturer, who will attempt to download prerecorded data from the unit.

"The housing of the memory unit may look good, but we don't know what's going on inside," Poormon said. "If data is unrecoverable, the unit fails the test."

Keeping black box data safe during a crash event will help make flying safer in the future. "The chances of a black box surviving a crash have increased greatly over the last decade," Poormon said. "Investigators can use data from the black boxes to rule things out, as well as determine what caused the problem," which could result in additional training for pilots, equipment redesigns or repairs to an entire fleet.

March 1, 2001

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