Investigators on Friday studied the crash scene where a Southwest Airlines jet trying to land amid heavy snow plowed off a Midway International Airport runway and into a street, killing a 6-year-old boy in a car.

Ten other people, most of them on the ground, were injured in the Thursday evening accident, the first fatal crash in Southwest's 35-year history, authorities said. The airport reopened Friday after being closed overnight.

Flight data and cockpit voice recorders were removed from the plane and sent to Washington for analysis, National Transportation Safety Board member Ellen Engleman Conners said, adding that the investigation would take at least a year.

Southwest Chief Executive Gary Kelly said the plane had undergone a routine maintenance check Wednesday in Phoenix. "There were no indications that the aircraft was experiencing any kind of maintenance problems," Kelly said.

The flight from Baltimore was the first of the day for the pilot, a 10-year Southwest veteran, and the co-pilot, Kelly said Friday.

Flight 1248 from Baltimore with more than 100 people aboard touched down around 7:15 p.m. Thursday. Though the airport had about 7 inches of snow, aviation officials said conditions at the time were acceptable.

The plane went off the end of the runway and slammed through a fence before striking the two vehicles, pinning one beneath it. The boy who died, one of five people in the pinned car, was identified as Joshua Woods of Leroy, Ind.

Southwest officials have been in contact with Joshua's family, airline spokesman Ed Stewart said.

The Boeing 737, nose resting on the ground, and the vehicles remained in the street Friday morning as NTSB investigators began work on scene.

The airport, surrounded by homes and businesses, has shorter runways than most major airports because it was originally built to handle smaller, propeller planes. Larger planes land at O'Hare International.

In a briefing, Conners stressed that a variety of factors need to be looked at before any cause is determined.

"Often, the first guess is not correct," Conners said. "So, we're not going to guess. We're going to focus on facts and science and data." Among other things, routine toxicology tests on the pilots were planned, she said.

Five crew and 98 passengers were aboard the plane, authorities said. Most were evacuated through the plane's inflatable slides in blowing snow, while others used stairs at the rear of the plane, Fire Department spokesman Larry Langford said.

Mahdi Abdelqader, a tow truck driver who saw the crash and raced to the scene, said Friday the people in the car were screaming for help.

"I didn't know what to do. I wanted to help them, but at the same time I was scared because I thought at any moment the plane could go up in flames," said Abdelqader.

Passenger Mike Abate, 35, of suburban Milwaukee, said that from within the plane, he could see that a man was carrying an injured child, and other people were taken away in an ambulance.

"We were safe on the plane," Abate said. "The toughest part was to realize that someone was under the belly of the plane."

Two people remained hospitalized at midmorning Friday, including one of the people in the car with Joshua. That person's condition was withheld at the request of family, Advocate Christ Medical Center said. A second person, in the other car that was hit, was in good condition at Holy Cross Hospital. Two passengers on the plane and six other people in the two cars were treated and released.

In February, a corporate jet skidded off a runway while taking off at Teterboro, N.J., crossing a highway and slamming into a warehouse. No one was killed, but a passenger in a car that was struck was critically injured.

A measure signed recently by President Bush will require hundreds of airports to improve the safety margin at the end of runways by 2015.

The Midway accident happened 33 years to the day after a crash of a plane approaching the airport killed 45 people, two of them on the ground. Eighteen other passengers survived. Among the dead were Dorothy Hunt, the wife of Watergate figure E. Howard Hunt; CBS newswoman Michele Clark; and Rep. George W. Collins, whose widow, Cardiss, succeeded him in office and served more than 20 years.