AUSTIN, Texas—Flight cockpit recorders can carry more than the voices of pilots in distress; they can register telltale sounds from the aircraft engines and structure, says University of Texas at Austin aerospace engineer Dr. Ron Stearman.
These recorders, when retrieved from downed aircraft, can provide valuable clues about the cause of a crash. But Stearman believes they can be used in routine maintenance checks as a tool to head off potential airline disasters.
Through his research of the 1991 crash of a small commuter plane off the coast of Rhode Island, Stearman has determined that cockpit recorders can help aircraft mechanics detect structural and mechanical problems.
It requires a trained ear or a computer to identify the sounds, but Stearman believes if someone had identified them on the 1991 flight, the plane would never have crashed.
Stearman’s findings will be featured in a Discovery Channel program titled “Crash Detectives” at 7 and 10 p.m. Tuesday, March 2 and again at 3 p.m. Sunday, March 7.
His research also will be archived in the Smithsonian Institution’s Permanent Research Collection beginning April 12. In addition, Stearman’s work has been nominated for the Computerworld Smithsonian Awards, to be announced June 7.
Three pilots aboard the Business Express training flight were killed when the Beechcraft 1900C turboprop crashed into the Atlantic Ocean off the coast of Rhode Island. The National Transportation Safety Board (NTSB) ruled the plane went down because of pilot error.
But the Airline Pilots Association (ALPA), which has authority to investigate crashes along with the NTSB, determined from the wreckage that the plane’s right engine had broken off in flight and had crashed into the tail section of the aircraft.
By studying the cockpit voice recorder, Stearman was able to verify ALPA’s finding. Stearman based his determination not on the pilots’ conversations, because they gave no hint of the impending mechanical disaster. Instead, he analyzed the flight recorder for background noises made by the aircraft itself.
What he heard confirmed that the right engine broke loose and the aircraft disintegrated. ALPA investigators later determined from the wreckage that the right wing was severed and the runaway engine and propeller cut through the tail section. Three of the four tracks on the recorder were miked to the pilot, copilot and general cabin area. A fourth track was unused.
Stearman found sounds on all four tracks showing the aircraft was experiencing whirl flutter, a phenomenon that occurs when hidden structural damage weakens a plane’s engine support structure to the breaking point. In this case, a damaged engine mounting structure resulted in the propellers wobbling so severely that the engine broke free of the wing.
The most telling information came from the unused fourth track on the recorder. Although this track was not miked, the recorder’s wiring acted as a primitive microphone that picked up sounds from the aircraft’s vibrations. The sounds on the fourth track matched some of the plane’s engine vibrations and æ along with the other tracks — ultimately indicated a final explosion.
Stearman also studied Federal Aviation Administration inspection records and learned that the Beechcraft 1900C had a long history of engine truss mount cracking, resulting in at least six redesigns.
“Commercial airline travel will double in the next 10 to 15 years,” Stearman said. “If commercial airline accident rates remain at today’s levels, then we can expect about one commercial flight crash a week. This tool can greatly enhance the safety of the traveling public.”
Stearman said the technology possibly could be used for spacecraft, as well.
Stearman worked on the project with Glen Schulze, former chairman of the Subcommittee on Instrumentation Recording/Reproduction of the Institute of Electrical and Electronic Engineers; Stuart Rohre of UT’s Applied Research Laboratory; and Monte Buschow, a former UT graduate student in aerospace engineering.
The team’s findings resulted in ALPA filing a petition asking the NTSB to reverse its decision that pilot error caused the 1991 Beechcraft crash. That petition was filed in June 1997, but the NTSB has yet to make a ruling.
The ALPA petition and Stearman’s investigation were triggered, in part, by Jack Murphy, whose son, John Murphy Jr., was the pilot in command on the Beechcraft. Murphy, who lives in Orange, N.J., said he became suspicious of the NTSB ruling on the crash after he saw the aircraft wreckage. Murphy said the slight damage to the right wing indicated it likely broke off the plane before impact.
The concept developed by Stearman and his team needs further research before it could be used on flight lines. The key project, the professor said, is to catalog the audio “fingerprints” of the various sounds occurring on an aircraft. The catalog would be fed into what Stearman calls an interrogator computer, which would be used by an aircraft mechanic to run diagnostics on flight recordings.
Such procedures could be implemented only after endorsement by the airlines and the Federal Aviation Administration and after aircraft mechanics and maintenance personnel had been trained.