CHICAGO – The reverse thrusters that should have slowed a Boeing 737 before it slid off a runway and into a busy street didn’t appear to have been working properly, federal investigators said Saturday after interviewing the pilots and crew.

The flight attendants said they could tell the Southwest Airlines jetliner wasn’t slowing after it touched down in the snow at Midway Airport Thursday, and the pilots said they applied the brakes manually as soon as they realized something was wrong, said Robert Benzon, National Transportation Safety Board investigator in charge.

“They all said it was a smooth landing, but they could sense a lack of deceleration,” Benzon said.

The plane, with 98 passengers aboard, slid off a 6,500-foot runway, through a fence and into street traffic, where it hit two cars and killed a 6-year-old boy riding with his family. Ten people, most of them on the ground, were injured.

Investigators are still trying to determine how much of a role the braking equipment played in the accident.

Because of blowing snow, none of the air traffic controllers saw the plane land, but more than 10 cameras have been identified that could provide additional information, including details about runway conditions, Benzon said.

On Saturday, workers used a crane with a sling to lift the damaged airliner off the city street and into a hangar for further inspection. The plane’s voice and data recorders already have been sent to Washington, D.C., for analysis, NTSB member Ellen Engleman Conners said.

Southwest said the captain piloting the plane has been with the airline for more than 10 years, and the first officer has flown with Southwest for 21/2 years. It was the first fatal crash in the airline’s 35-year history.

Though the airport had about 7 inches of snow at the time, aviation officials said conditions were acceptable. Southwest chief executive Gary Kelly said Friday that the plane had recently had a maintenance check and showed no signs of problems.