Air-Crash Sleuths Tease Clues From Black Boxes’ SilenceAlan Levin
Investigators had no data to work with or survivors to interview after professional golfer Payne Stewart’s private jet slammed into a South Dakota field in 1999. The cockpit recorder yielded 30 minutes of no voices.
Nothing, in this case, meant something. The lack of human activity meant the crew had probably passed out from lack of oxygen, according to U.S. National Transportation Safety Board records. A horn warning that the cabin had lost pressure could be heard in the background.
Investigators into the disappearance of Malaysian Air Flight 370 similarly will have to resolve the longest disappearance in modern airline history in part from what isn’t there, even if the Boeing Co. 777-200ER’s two recorders are found at the bottom of the Indian Ocean.
They probably won’t hear the moment the plane carrying 239 passengers and crew turned off course March 8 while flying to Beijing from Kuala Lumpur, as its voice recorder would have picked up only the last two hours of conversations. They will have at least 25 hours of data about the flight path and how aircraft functioned, possibly enough to reconstruct what happened in the cockpit without hearing a word from the pilots, said Steve Wallace, former chief of the U.S. Federal Aviation Administration’s investigation arm.
“These skilled investigators can draw inferences about human behavior from what they see on the data recorder as well as what they hear on the voice recorder,” Wallace said.
Searchers working under contract for the U.S. Navy launched an unmanned submarine yesterday to survey the ocean depths for signs of wreckage from Flight 370 and, in particular, the flight-data and voice recorders.
A search team aboard the Australian vessel Ocean Shield has identified acoustic pings from the ocean floor that it believes are from the plane’s recorders, according to Prime Minister Tony Abbott. The pingers activate once a black box is submerged in water.
Known as black boxes, the two recorders on commercial airliners are painted orange to make them more visible in a crash site. They are encased in layers to protect against impact force, fire and water damage.
Pilots almost never narrate the events leading up to an accident, so investigators examining cockpit recorders have had to become more inventive, said Vernon Ellingstad, former director of research and engineering at the NTSB. They listen for switches, alarm chimes and other background noises, he said.
The data recorder on the 777 stores hundreds of data parameters, including position and altitude, engine performance, function of flight control surfaces and how the autopilot is being programmed.
The data recorder “has got all of the current control inputs and control surface responses,” Ellingstad said in an interview. “You can really account for how it was flown and the controls to the autopilot and so forth. That should be accounted for with pretty decent fidelity.”
The data recorder will help investigators understand whether the plane was being hand-flown or was commanded by autopilot as it turned around while flying to Beijing, Wallace said.
It may also show whether pilots or someone in the cockpit shut off the transponder, a radio beacon that identifies planes to radars on the ground, or it malfunctioned. A second system that transmitted text messages and data about engine performance via satellite also stopped functioning.
Equally important is what the data recorder can rule out.
Because it records any malfunctions or alerts that are shown to pilots, it will show whether there was a fire or mechanical breakdown that may have prompted the turn.
NTSB files include many instances in which investigators resolved mysteries without help from one or both recorders.
On Jan. 13, 1982, an Air Florida Boeing 737-200 crashed into a bridge and plunged into the Potomac River shortly after taking off from Washington, killing 74 people on the plane and four motorists.
The plane had an older data recorder that stored only five parameters on a silver foil strip, forcing investigators to turn to the cockpit voice recorder to figure out how the engines were performing.
Investigators analyzed the frequency of the hum picked up by the voice recorder to calculate how fast the engines were spinning, according to the agency’s report. The plane had never gotten to full takeoff power because of snow and ice, the agency concluded.
After TWA Flight 800 exploded off the coast of Long Island on July 17, 1996, killing all 230 aboard, the NTSB found that the explosion had cut power to the recorders.
The voice recorder captured a fraction of a second of explosion sounds. Investigators concluded it was consistent with a fuel tank blowing up, according to the agency’s report.
The worst-case scenario in the Malaysian probe is if whoever flew the plane toward one of the world’s most remote regions disabled the recorders, which may be possible by switching off circuit breakers that provide power to the devices, Ellingstad and Wallace said.
Even that would leave clues, they said.
“Obviously, if someone hit the circuit breakers, you’d see that,” Ellingstad said. “You’d know when it was. That certainly would strongly suggest some kind of malicious intent.”