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| DIVE TEAM AT WORK Successful Recovery After Mid-Air Crash |
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08/31/09
Our divers were aware that the area of the Hudson where the plane’s fuselage entered the water on August 8 represented the most dangerous elements that an evidence recovery diver could face: deep water, shifting currents, zero visibility, and entanglement hazards. Divers knew this because just a few months prior they had recovered a lost engine from US Airways Flight 1549 following its emergency landing in the river after striking a flock of geese.
During the Flight 1549 operation, our divers and the New Jersey State Police combined their resources—a partnership that led to a successful recovery. The state police operated a side-scan sonar system to initially locate the lost engine, and we followed up with sector-scan sonar to pinpoint the engine’s location. This same joint operation was used in the recent mid-air collision to locate the victims and the plane’s missing fuselage.
Side-scan sonar—known as a “towfish”—is a torpedo-like device towed behind a boat. The towfish converts acoustic sound pulses into a video image of the river bottom. To a trained operator, the resulting image offers a photographic view of the bottom that can be used to identify items of evidentiary interest. Side-scan systems can cover large swaths of water in fairly short periods, typically a square mile per day. They can also provide clarity in zero-visibility conditions—when the murkiness of the water makes it impossible for divers to see with their eyes. The state police team reviewed many hours of side-scan data they gathered after the crash and provided our divers with a general location of what looked like the fuselage of a small plane. Armed with this information, on August 9 we deployed a sector-scan system to verify the target and to identify its location. Sector-scan sonar also uses sound pulses to create a visual image. The difference between the two systems is that sector-scan sonar is housed in a six-foot-high tripod that is lowered to the river bottom. Once it is stationary, a transducer rotates in a 360-degree path to paint a real-time picture of the immediate surroundings. Since the location of the tripod is known, precise GPS points can be plotted from the surface.
This sonar can also show the position of a diver, who can then be directed to a specific target through underwater communications systems. In this case, our sonar operator located the same object that was scanned by the state police sonar operator and was able to direct a diver—despite a strong current and zero visibility—to the wreckage. Once the plane was identified, the team turned its efforts to marking the wreckage for recovery. To accomplish this without risking a diver in high current, the sector scan was utilized again. After a dozen or more attempts, we deployed the tripod successfully, and state police divers were able to drag a large weight alongside the plane. They were then able to provide a direct line from the plane to the surface. A crane provided by the Army Corps of Engineers was used to lift the wreckage from the water. In the end, the combined efforts of local, state, and federal agencies—the National Transportation Safety Board, the New Jersey State Police, the New York Police Department, the Army Corps of Engineers, and the FBI—led to the safe and successful recovery of the wreckage and of the remains of all the victims of this tragedy. Resources: |
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