As investigators expected, the cockpit voice recorder from the shattered Learjet has yielded various noises but no voices from the final moments of the doomed flight.
However, the noises on the tape could help in the investigation into what caused the Learjet to crash Oct. 25 in northeastern South Dakota, National Transportation Safety Board spokesman Paul Schlamm said Thursday.
"There are various sounds and noises we're working on. We are hopeful that will lead to some useful information that will help in the investigation," Schlamm said.
Investigators had expected to hear no voices on the cockpit voice recorder because it has a 30-minute loop that records over itself. They believe that the two pilots and four passengers likely died hours before the plane crashed.
The plane crashed into a pasture near Mina four hours after it left Orlando, Fla., for a flight to Texas. It flew 1,400 miles across the country, apparently on autopilot, before it ran out of fuel.
Government officials are looking into the possibility that the jet lost cabin pressure soon after taking off, causing everyone on board to die or lose consciousness from lack of oxygen.
The recorder was damaged extensively when the plane hit the ground at an estimated speed of 600 mph. It was sent to Seattle so its manufacturer could help recover information from the recorder's memory chips.
Investigators recovered most of the airplane parts from the crash site, and the wreckage is being stored in an airport hangar in nearby Aberdeen, Schlamm said.
Investigators found some additional wreckage Sunday when they used metal detectors to make a final sweep of the field where the plane crashed, Schlamm said.
The NTSB likely will not issue its findings about the cause of the crash for at least several months, he said.