A skirmish between American Airlines and Airbus SAS yesterday at a hearing on last year's crash of American Airlines Flight 587 illustrated again the inevitable conflict between the search for truth in the crash investigation process and the search for blame in court.

Few crashes showcase the conflict better than the investigation of Flight 587, in which the vertical tail fin of the wide-body Airbus A300-600 tore off shortly after takeoff from John F. Kennedy International Airport in New York on Nov. 12, 2001, sending the plane crashing into a neighborhood in Queens and killing 265 people.

Three days into hearings on the crash by the National Transportation Safety Board, it is becoming apparent that there is no clear villain in this crash, one of the worst in U.S. history. The safety board will take months to analyze the crash and find a probable cause. But testimony so far indicates that the crash resulted from a failure to adequately communicate to pilots that multiple rudder reversals could tear off an A300-600's tail, complicated by a series of rational decisions and assumptions that turned out to be wrong.

In court, however, there must be a villain.

For that reason, witnesses for American and Airbus have on the surface attempted to make their legal points during the hearings while adhering to the safety board's rules limiting testimony to facts and documentation. Airbus has questioned whether American's pilot training overemphasized use of the rudder in recovering from in-flight upsets, while American has questioned the plane's design and whether Airbus gave adequate warnings about potential stress on the rudder.

But yesterday, American apparently believed that Airbus had stepped over the line by asking detailed questions about a 1997 internal e-mail. In that communication, an Airbus employee outlined American's complaints that the aircraft manufacturer was using flight data in court against American in a lawsuit stemming from a turbulence incident in the early 1990s.

That incident had nothing to do with the investigation then under way of a series of violent, in-air gyrations on May 12, 1997, that forced an American flight to Miami to make an emergency landing in Fort Lauderdale.

"AAL [American] flight safety has informed me they will not give me the DFDR [digital flight data recorder] from the subject incident," said the e-mail from an Airbus employee to Airbus headquarters in France. "Furthermore, AAL flight safety informed me that they will probably never again release the DFDR to Airbus."

Because the e-mail seemed to portray American refusing to cooperate in a crash investigation, American yesterday attempted to introduce another e-mail, from the same Airbus employee, saying that Airbus's use in court of the flight data recorder information from the earlier incident had left him "in an extremely sensitive situation, and our credibility is going down the toilet fast."

Neither e-mail appeared to have a direct relationship to the crash of Flight 587. But lawyers for both sides were suddenly active with intense conversation, threatening to release other documents that could start a battle of the memos.

The safety board's acting chairman, Carol J. Carmody, cut the battle short, refusing to allow the second e-mail to be entered into the investigation docket.

Senior board officials said the dust-up probably wouldn't affect the 587 investigation but that it illustrated an escalating conflict between the adversarial legal process and an investigative process that relies on parties sharing information. They said some witnesses are reluctant to give information to the board for fear they will subject themselves or their company to liability.

Lawyers are getting into the investigative process far quicker than in the past, they said. "We're getting freedom-of-information requests before the smoke clears," one official said.

George W. Black, a member of the safety board, said, "Sometimes it slows down our investigations because people are reluctant to give us things till they run it through their lawyers."

This is not a new problem. The nonprofit Rand Corp. warned several years ago that the legal process could damage the crash-investigation process.

"It's to be expected in today's legal climate," said Gregg Overman, director of communications for the Allied Pilots Association, the union that represents American Airlines pilots. "I wouldn't want to characterize it as all bad" because the legal system can help victims and their families.

"Does it serve the broader interests of the traveling public and the pilots?" Overman said. "Probably not."

John Cox, executive air-safety chairman of the Air Line Pilots Association, which represents most of the country's pilots, said the U.S. investigative process is so strong that it can fend off any threat from the legal process. Both processes are adversarial and in their own way focus on finding out what happened.

"The truth tends to withstand that process," Cox said.

Robert Benzon, investigator in charge at the National Transportation Safety Board, narrates the final moments of American Flight 587.