After deciding it was safe to land in a snowstorm, the pilots of Southwest Airlines Flight 1248 overran the zone where the plane needed to

 touch down and lost hundreds of feet of runway that would have helped stop the jet before it skidded outside the airport and killed a 6-year-old boy, federal investigators said Thursday.

The plane glided over the runway, wasting precious stopping distance, before the captain planted the landing-gear wheels more than 2,000 feet beyond the edge of the 6,522-foot runway. The pilots needed at least 800 more feet of runway to avoid a collision, according to the National Transportation Safety Board, which released a report Thursday updating the status of its investigation.

As they approached the airport Dec. 8, the pilots and a Southwest dispatcher were confident a landing could be accomplished, despite contending with low visibility, a nettlesome tailwind chasing their plane and reports of poor braking power on snowy Runway 31 Center, they later told NTSB investigators.

The pilots based their decision to land on the dispatcher's positive assessment, their piloting experience and flight data they entered into a cockpit computer, investigators said. Weather updates indicated a freezing fog was setting in, but the computer confirmed the difficult landing would be within the capability of the Boeing 737-700 and would conform to Southwest's procedures.

The 59-year-old captain, who was flying the plane, missed the landing zone, according to the report.

Preliminary calculations, using radar information and the flight data recorder onboard the plane, show the aircraft touched down with about

 4,500 feet of runway remaining,. The aircraft needed about 5,300 feet of stopping distance under the slick conditions to avoid a collision, the report said.

It also is unclear whether it was legal for Southwest Flight 1248 to land in the heavy snow.

About 20 minutes before the accident, visibility was only one-half mile--less than the three-quarter mile of visibility the Federal Aviation Administration requires for an approach to 31 Center, the report said. Making a landing with only a half-mile of visibility would violate FAA regulations.

The safety board did not provide the visibility reading at the time of the accident. But about 23 minutes after the accident, "a special observation revealed'' that visibility was only one-fourth mile, the safety board said.

An attorney for the Woods family said the safety board's report gives him grounds for a lawsuit that holds Southwest and the city of Chicago responsible for the accident.

"What this says is that there shouldn't have been a landing. The flight should have been diverted. The fallacy here is that the aircraft can land in a snowstorm," Ronald A. Stearney Jr., the lawyer, said. "Given the egregious nature of what we're finding out, there's only one thing to do--for Southwest to admit liability. They ought to come to the table and help this family put this behind them."

The Woods family's reaction to the safety board's report was "that Southwest murdered Joshua," Stearney said.

Air-traffic controllers who were in the Midway tower Dec. 8 told investigators they did not see the plane land, but they spotted the aircraft's lights penetrating the falling snow and ground fog.

The plane hit the runway at 152 m.p.h., investigators said. It bounced and became momentarily airborne again during the

 29-second landing attempt.

The aircraft's thrust-reversers, which help the automatic-braking system the pilots used to stop the plane on the ground, were not functional until more than midway through the landing, investigators said. The delay was much longer than the safety board previously reported, based on interviews with the pilots two days after the crash, the first fatal accident in Southwest's history.

After slipping off the runway, the plane carrying 98 passengers was slowed by rolling through a fence designed to absorb jet blasts, an airport perimeter fence and onto the street, where it hit two vehicles. The impact killed Joshua Woods, 6, of Leroy, Ind., who was in one vehicle with his family en route to visit his grandmother.

From the time the plane landed to when it came to an abrupt, colliding stop, it traveled about 5,000 feet, the safety board said.

It remained unclear whether the failure of the thrust-reversers was caused by a mechanical problem or possible pilot error. The safety board is testing the thrust-reverser systems.

The captain told investigators he had trouble moving the lever that activates the thrust reversers, which are supposed to begin working as soon as activated upon landing. In a separate post-accident interview, the first officer said he reached over after "a few seconds" and was able to engage the lever for the thrust reversers.

But data from the plane's flight data recorder now show the thrust reversers did not activate until about 18 seconds after landing, the safety board said.

Many pilots who have flown into Midway during inclement weather have questioned the judgment of the Southwest crew. The update from the NTSB did not alter their views.

"My question is very simple, Mr. Captain. Why did you decide to land on that airport when the runway conditions were at a bare minimum and there was a tailwind component?'' said Javed Sheikh, 60, a retired commuter airline pilot who flew for 26 years.

"There was no impending emergency, no compulsion that evening for anybody to land on that runway,'' Sheikh said.

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Tribune staff reporter Andrew L. Wang contributed to this report.
jhilkevitch@tribune.com