In January 1999, a former employee of an upstate New York company that makes steel cable for the control systems of passenger jetliners and military aircraft approached federal prosecutors with a startling story. The company, she said, had sold the cable for years without performing the tests required by its most demanding customer, the United States military, and did not even own the equipment needed to detect flaws in its product. The accusations were potentially serious. Models of many widely used airplanes, including the Boeing 737, use steel cable to connect cockpit controls to the engines, landing gear, rudder and wing surfaces. The company's customers included the United States Air Force and more than a dozen American and foreign airlines, and the company had been selling cable for years. Federal criminal investigators quickly verified the outlines of the former employee's account. They immediately notified the Department of Defense, and the Federal Aviation Administration learned of the possible danger soon after. But the responses were starkly different.

  Military officials immediately tested samples of the cable, found that they began to break at barely half the load they were supposed to support, and started inspections of all aircraft equipped with it. In August 1999, Air Force mechanics replaced cable linked to the engine controls of a backup plane to Air Force Two, which is used by Vice President Al Gore. The F.A.A., by contrast, did no tests and did not inform the airlines about the possible problems for nearly a year, during which several carriers continued to use cable sold by Strandflex, the upstate company. The aviation agency finally published a notice about the issue on May 18, a day after a New York Times reporter first raised questions about the case. The agency said the timing had been coincidental. The notification was merely a warning, and it did not require airlines to act. But soon after, American carriers, including Southwest and Trans World Airlines, began a special inspection of all Strandflex cable they had. Southwest has begun removing it from 47 aircraft, roughly 15 percent of its fleet. Strandflex has not been charged with wrongdoing. In documents filed with the Securities and Exchange Commission, it has acknowledged it is the target of a criminal investigation and has said it intends to fight a civil lawsuit brought by the former employee, who stands to receive a percentage of any damages the government might recover. The company would not comment further about the matter. Government officials have reviewed records of accidents and say there is no evidence of any major accidents caused by cable failures. Reports at the National Transportation Safety Board, though, include incidents in recent years in which broken or frayed cables forced pilots to take action to land planes safely. The board has attributed the failures to poor maintenance, and has not investigated who made the cable involved in the incidents.

Those reports appear to support what several aviation experts said in interviews: that a well-trained pilot should, by using other controls, be able to compensate for the failure of a single control system tied to the cables. The experts noted that planes typically have backups, so that a pilot can steer even if a cable snaps. Still, experts said, they could imagine situations in which snapped cables could seriously challenge a pilot. In interviews over the past month, the F.A.A. offered conflicting explanations why it had taken nearly a year to tell the airlines about the cable. First, officials insisted there was no evidence that the cable had been sold to airlines. Then they acknowledged that it had been sold to at least several major carriers, but they said it was not a critical component. Its failure, the officials asserted, could not cause an accident. The F.A.A.'s views startled several aviation experts, including Michael Peat, a safety specialist at the International Association of Machinists and Aerospace Workers, who said control cables were among the most critical parts of the aircraft. Mr. Peat said maintenance workers paid particular attention to the condition of the cables. If one breaks, he said, "it is dangerous." "These are what are considered the primary flight controls of the airplane," he said. Critical components like control cables, Mr. Peat noted, are subject to special inspection requirements. The mechanic who installs or services the cable cannot review the work; another mechanic or an inspector must do it.

Captain John Cox, vice chairman of the Airline Pilot Association's safety committee, said pilots were trained to react when ailerons fail and typically would be able to maintain control of the aircraft using other steering systems. He said losing a single system, like an aileron, would not be life threatening. But Captain Cox, who flew 737's for 15 years, said it would be a mistake to say a failed aileron cable was not a serious problem. "Flight controls are something you take very seriously," he said. Patricia A. Keehle went to work for Strandflex on Jan. 1, 1998. As a quality assurance manager, she made sure that Strandflex performed tests on the aviation cable it sold to the military and other customers. Ms. Keehle left Strandflex that August. It is unclear why she left, and her lawyers said she did not want to comment further. On Jan. 22, 1999, Ms. Keehle sued Strandflex in Federal District Court in Syracuse, claiming that the company had defrauded the government by certifying that it had performed the inspections and by using improper material to make the cable. She said the company was supposed to use an approved lubricant to coat the cable, but substituted an untested brand. Ms. Keehle said the lubricant was "critical to the quality of the cable," and was supposed to function at extreme temperatures. But she said that when the company tested the cable with the new lubricant at room temperature, it failed. Paul E. Dixon, senior vice president and general counsel for Strandflex's parent company, Handy & Harman, would not comment on the case, although he said the company was talking with the government.

Documents filed with the Securities and Exchange Commission said that the company was cooperating with the government investigation and that "there are no known incidents of any Strandflex wire failing and causing personal or property damages in any application." Ms. Keehle filed her lawsuit under the Federal False Claims Act, which allows whistleblowers to sue their own companies and collect part of the damages. After a preliminary investigation, federal prosecutors in Syracuse notified both the Department of Defense and the F.A.A.'s parent agency, the Department of Transportation. In May 1999, the Department of Defense issued a warning about Strandflex cable that it sent to other federal agencies. Federal prosecutors said the F.A.A. was one of the agencies notified. Once the Air Force received the notice, it began to inspect its planes, according to Major Chet Curtis, an Air Force spokesman. He said that in August 1999, workers removed Strandflex engine control cable from a backup plane to Air Force 2. The agency's account of how it handled the case raises as many questions as it answers. Margaret Gilligan, the F.A.A. deputy administrator for regulation and certification, said agency officials did not learn of the problem until August 1999. Ms. Gilligan said that in September 1999, the agency sent an investigatorto Syracuse to evaluate the importance of the cable and make recommendations.

The F.A.A. initially concluded that the cable was a critical part, assigning the case its highest level of urgency. But Ms. Gilligan said in a recent interview that the conclusion changed after the investigator learned more about the cable and its function. Ms. Gilligan said the investigator recommended that airlines be notified. But she said that he did not recommend that the agency issue its most urgent warning, an Airworthiness Directive, which would have required airlines to fix any problems. "That is an indication it was not a safety-of-flight issue," she said. Ms. Gilligan said there were several reasons for the lack of urgency. The F.A.A., she said, reviewed its records and could find no reports of problems with Strandflex cable. In addition, she said, the department's experts believed that because pilots could continue flying the plane if a cable broke, it was not a crucial part. During the next several months, Ms. Gilligan said, the agency tried to determine whether Strandflex cable was ever used by airlines and found no such evidence. On May 18, a day after a New York Times reporter called about the issue and two months after Ms. Keehle's lawsuit was unsealed in a Syracuse courtroom, the F.A.A. posted a notice about Strandflex on its Internet site. The posting disclosed the Department of Defense tests on the cable's strength and said investigators had also found kinks in samples of the cable. Ms. Gilligan said the reason the F.A.A. took several months to post the notice was that the agency wanted to make sure it had all the information, including the Department of Defense test results, before acting. "In October when the investigator recommended going this route, we did not have these details," she said. "In May, when we were able to include that information, it was timely to send out one of these unapproved parts notifications."