Investigators returned Tuesday to the wreckage of a Continental Airlines jetliner that veered off a runway, rushing to collect evidence ahead of snow expected to move in later in the day.

One group was working Tuesday inside the charred fuselage of the plane to document its condition, National Transportation Safety Board spokesman Peter Knudson said.

Authorities are trying to determine why an odd bumping and rattling noise was heard on the flight's recorders in the seconds before Saturday's crash, which injured 38 people at Denver International Airport.

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The noise was detected 41 seconds after the jet, bound for Houston, started speeding down the runway. Four seconds later, one of the crew members called for the takeoff to be aborted, said Robert Sumwalt, another NTSB spokesman.

The recording ends six seconds after that, probably because the plane slammed to the ground after hurtling off an embankment, he said.

Sumwalt revealed the findings from the initial review of the flight data and cockpit voice recorders on Monday. Experts planned to begin a more in-depth analysis of the contents of the recorders in Washington, D.C., on Tuesday.

All 115 passengers and crew members escaped the jet, which caught fire on the right side. Four people remained hospitalized Tuesday, one of them in serious condition.

Sumwalt said investigators have found no problems with the plane's engines, tires or brakes, but they are not yet ruling anything out.

The plane traveled about 2,000 feet after leaving the runway, crossing a grassy strip and a taxiway before going off the embankment, hitting the ground at its base. It then went up a slight hill, over an access road and then down another small hill on the other side of the road before landing on its belly, its landing gear shorn off.

Lead NTSB investigator Bill English said the plane's flight data recorder shows the thrusters on both engines were switched to reverse. He said that normally happens when crew members try to stop a takeoff.

Sumwalt said investigators are still gathering information about the exact wind conditions on the runway at the time of the accident. However, he said the cockpit voice recorder contained no comments about wind.

Investigators have not yet interviewed the plane's captain, who was flying the plane and was among the injured. Authorities have not disclosed his condition, but Sumwalt said he is physically unable to be interviewed. They have talked to the first officer, who said the plane began moving off the center of the runway as it reached about 103 mph while speeding down the runway for takeoff.

The plane continued to accelerate, reaching a maximum speed of about 137 mph, Sumwalt said.

Off-duty crew members who had flown the plane earlier in the day also were on board at the time of the accident, and Sumwalt said the first officer from that crew returned to the plane three times to help rescue passengers. Sumwalt also reported that those crew members said they had no problems with the plane during their flight.

A fire charred and ripped open much of the right side of the plane, with the worst damage around a crack around the fuselage. Sumwalt said all the passenger seats remained intact during the plane's wild ride off the runway, although seats in row 18, near the crack, had loose fittings.

Sumwalt said the runway was bare and dry when the plane attempted to take off and no debris was found there.

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