A combination of thick snow and relatively short runways at Midway International Airport can make landing a plane a daunting task for even veteran pilots, requiring precision and allowing scant room for missteps.

After Thursday's deadly runway accident involving a Southwest Airlines jet at the hemmed-in airport, some experts are calling for new buffer zones or other safety measures to give pilots at Midway and hundreds of other airports a wider margin for error.

The Boeing 737 was landing in a snowstorm when it slid off the end of the runway, plowed through a fence and struck two cars near a busy intersection. A 6-year-old boy in one of the cars was killed and 10 people, most on the ground, were injured.

"His father looked out and saw a turbine engine turning right outside his window," Ronald Stearney Jr., the attorney for the family, said Friday.

The National Transportation Safety Board said the cause of the accident was under investigation. The plane's voice and data recorders were sent to Washington for analysis and hold "pristine" information for investigators, NTSB member Ellen Engleman Conners said.

But much of the attention initially focused on the 6,500-foot runway. Midway — built in 1923 and surrounded by houses and businesses — is among nearly 300 U.S. commercial airports without 1,000-foot buffer zones at the ends of its runways. Most lack the room to create adequate buffers.

Safety experts say such airports can guard against accidents by instead using beds of crushable concrete that can slow an aircraft if it slides off the end of a runway.

The concrete beds — called Engineered Material Arresting Systems — are in place at the end of 18 runways at 14 airports. They have stopped dangerous overruns three times since May 1999 at John F. Kennedy International Airport in New York.

"We think it's incumbent on airports that don't have the room for these safety areas to at least put in one of these systems," said Jim Hall, NTSB chairman from 1993 to 2001.

Hall said the lack of a 1,000-foot overrun area and the absence of the concrete beds would likely be a focus of the investigation.

"It's a tragedy that did not have to occur," he said.

A recently passed federal law seeks to encourage more airports to build concrete beds or extend their runway barriers by requiring them to do one or the other by 2015.

Chicago Department of Aviation spokeswoman Wendy Abrams could not immediately say whether an arresting system had been considered at Midway.

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

The plane's ground speed was 152 miles per hour as it landed and it hit the fence at about 46 miles per hour, she said.

Some pilots say relatively short runways like Midway's pose a challenge in icy or snowy weather, forcing them to touch down as close as possible to the beginning of the runway to allow more braking time.

"It's not a place you can be a little off," said Richard Ward, a retired United Airlines pilot who occasionally flew into Midway years ago. "You don't have the variable of a long runway to correct any errors."

Investigators will determine the exact spot where the plane touched down through simulation, Conners said.

Southwest said the 59-year-old captain piloting Thursday's flight has been with the airline for more than 10 years, and the 35-year-old first officer has flown with Southwest for 2 1/2 years. It was the first fatal crash in Southwest's 35-year history.

Some safety experts said the size of the runway should not be used as a scapegoat.

"It is not the runway length that's the issue," said Bernard Loeb, who was director of aviation safety at the NTSB during the mid-1990s. "Runways are either adequate or they're not."