American Airlines has long prided itself on its safety record. But after several crashes and other accidents in the past five years, the airline's chief safety official faced a day of difficult questions today as federal safety investigators continued their hearings into the lastest crash--a June 1 accident, during intense thunderstorms here, that killed 11 of the 145 people aboard.

After the crew pressed forward to land, the McDonnell Douglas MD-80 jet skidded down the wet runway and vaulted off the end. The captain was among those killed.

Robert W. Baker, vice chairman of American, spent most of his two hours of testimony before a National Transportation Safety Board panel discussing steps the company has taken to improve safety after the June 1 crash and a Dec. 20, 1995, crash at Cali, Colombia--disasters that he said had "literally rocked" the corporation.

"I certainly have gained a clearer understanding of some things American will address and improve," Baker said.

Testimony by the co-pilot Wednesday, plus reams of factual reports from the safety board, indicate that the crew of American Flight 1420 thought they had found a hole in the weather at Little Rock and did not fully comprehend the danger. They also apparently became overloaded with work as they performed a last-minute runway change approaching the airport--what pilots would call "getting behind the plane."

Investigators are exploring whether co-pilot Michael Origel and captain Richard Buschmann missed a key element of their landing checklist. The spoilers--flat panels on top of the wing that flip up on landing to aid in braking--did not deploy, and it is possible the crew never armed them to deploy automatically. Braking ability on a wet runway would drop by an estimated 70 percent without spoilers.

Baker established quickly today that he would not second-guess his pilots. He said in answer to a question from chief investigator Gregory Feith that it would be "grossly inappropriate" for him to offer any opinion on the decision-making. He added that he is not a pilot and said, "I'm not qualified to offer an opinion."

In several ways, Baker was walking a tightrope. His audience included not only plaintiffs' lawyers but also representatives of the Allied Pilots Association who are aiding in the investigation. Baker noted that the relationship between the airline and the union was poisoned by a 1999 strike, and the two are working to reestablish full cooperation on safety issues.

Baker said American's upper management structure had been altered to further emphasize safety. For instance, Baker has been elevated from executive vice president for operations to vice chairman with authority over all safety and operations functions. The safety department is being reorganized, and outside experts will be brought in more often to evaluate safety. By June, he said, the company will revise its thunderstorm-avoidance policy and its approach-and-landing policy.

"We've got some work to do," he said. "We'll be a better airline for it."

The safety board's chairman, Jim Hall, politely but pointedly noted that the Cali and Little Rock crashes were not American's only recent accidents. He pointed out the American Eagle crash at Roselawn, Ind., on Oct. 31, 1994, which is not included in American's statistics. American Eagle, a regional carrier, is owned by American.

As Baker sat and listened, Hall ticked off a list of other American Eagle crashes and a series of nonfatal incidents that damaged American and American Eagle planes. Recent American incidents include a plane that flew through a tree while attempting to land at Hartford on Nov. 12, 1995, a runway overrun at Cleveland on March 5, 1997, and a plane hitting a fence at Tegucigalpa, Honduras, on June 14, 1999.

Baker remained outwardly calm as Hall listed the problems, but friends said it was clear he was growing angry.

Today's testimony also concerned the weather, including an analysis of weather radar from the time around the crash that showed a "very large, very strong" thunderstorm was hitting the airport just as the plane touched down. George Wilken, science and operations officer for the National Weather Service's North Little Rock forecast office, said the center of a strong thunderstorm was just northwest of the airport as the plane touched down.

But the data indicate that the plane was not hit as it landed by a microburst, a mass of cold air that blasts downward from a thunderstorm and spreads strong winds outward from its center as it hits the ground. Wilken said a huge microburst did hit the airport minutes after the crash.

One of the key questions is what the crew knew about the weather--and when they knew it. The cockpit voice recorder and the co-pilot's testimony indicate the crew knew the weather was bad but thought they could get to the airport before the storm hit.