The discovery last week of the flight data recorder (FDR), the second “black box” at the crash site of Germanwings Flight 9525 in the French Alps has allowed investigators to shine more light on the Airbus A320's final moments, and precisely what inputs were made to its controls. Up until its discovery, all evidence as to the cause of the tragedy came from analysis of the cockpit voice data recorder (CVR), which purportedly was sensitive enough to note no change in the breathing of the co-pilot, who was believed to have locked the pilot out of the cockpit in a suicide attempt. Based upon the initial reports, the FDR unit has shown investigators that the flight controls were being methodically operated before the crash, supporting the theory that someone intentionally flew the A320 into the ground.
How much evidence can be gleaned from the badly battered FDR remains to be seen, but given the advances in black box technology over the past years, chances are good that it, like the CVR will continue to yield more information as to what really happened, according to Kevin Poormon, a senior research engineer and group leader for impact physics at the University of Dayton Research Institute. His lab has been testing black boxes for the major manufacturers for the past 25 years, putting them through punishment intended to exceed all but the worst cases, to help ensure the precious data they contain survives. “In most cases, and particularly in this event, it answers a lot of questions,” Poorman told AIN, adding the lab tests on the units should have exceeded the forces at play in the impact suffered by the Germanwings recorders. “If they had not recovered the cockpit voice recorder intact, they probably would still have been guessing about what happened. Did the pilot and co-pilot become incapacitated? Was it a terrorist takeover of the aircraft? All those questions would still be being asked right now if they did not have the information they got off the cockpit voice recorder.”
Any new model flight recording device must pass muster with the FAA, which has a strict list of parameters. Memory units must presently withstand severe peak impact on the order of 3,400g for 6.5 milliseconds, as well as survive specific parameters for fire, deep sea pressure and water immersion. For the impact test, which simulates the forces involved in an airplane crash, the device is bolted inside of a metal housing known as a sabot and fired at a velocity of 350 miles per hour from a 40-foot long, 12 inch diameter, compressed gas-powered cannon into aluminum honeycomb material which is carefully selected to meet the individual test parameters for achieving the specified G-force. Around the early 1990’s, the impact forces applied in the tests were increased, according to Poormon to “address these kinds of events where the planes were actually flown into the ground instead of an accident where it was on approach or take off,” as the impact is much more violent in those cases.
The part that concerns Poormon, who designs and conducts all the tests, is not whether the device survives the impact, but whether the test was valid in recreating that precise suite of conditions. In a successful impact test, the sabot comes to a stop in 18 inches in a span of just 6.5 milliseconds, as it crushes the honeycomb material. “The test is designed to be more severe than the unit would experience during a crash event,” said Poormon of the impact test which has changed little over the past quarter century. “That’s because black boxes have to survive, even if everything else doesn’t survive.”
After the test, the lab will pack the device along with high speed films showing the impact and a computer report, off to the manufacturer who will then evaluate if data is downloadable. “They have to recover essentially all of the data that was recorded on there prior to the test,” said Poormon. “If they can’t download or recover that data, then its considered a failure.”
While released photos of the FDR from Germanwings Flight 9525 show a crushed and blackened exterior housing, that is no indication of the quality of the data within, according to Poormon. “Black box manufacturers don’t care if the unit’s housing or the electronics don’t survive a crash,” he said. “Only the memory unit inside has to survive.”
Among the advances in design Poormon has noted over the past two decades is the increased information storage capacity of the units. “As our computers get more powerful and more compact, the amount of data that can be stored on these units becomes greater, so they can record more channels.” In addition to monitoring more aircraft functions, the problem of recording over pertinent information is now also less prevalent. “They used to be about half an hour of recording time, and now a lot of them are up to 25 hours,” Poormon said.