HB-IWF, the Swissair MD-11 which crashed in 1998, is seen in this 1997 photo. (George Tomaszewski/View Full Size)

But the investigators, wrapping up a 4-1/2 year probe into the accident, could not definitively say which wire was involved and said there was little the crew could have done to land the plane safely.

All 229 people aboard the McDonell Douglas MD-11 were killed when the Swissair flight, bound for Geneva from New York, crashed into the Atlantic Ocean on Sept. 2, 1998.

More than 250 kilometers (155 miles) of wire were installed on the plane, and investigators looked at some 2 million pieces of plane recovered from the seabed to determine the cause of the crash. Some 98 percent of the airplane by weight was recovered from wreckage 55 meters below the ocean surface.

"It's important to emphasize here, it is unlikely that this entertainment system power supply wire was the only wire involved in the lead arcing event," said Vic Gerden, lead investigator at the Transportation Safety Board of Canada.

"We strongly suspect that at least one other wire was involved... However we were unable to identify or place any of the arced wires in the area where we believe the fire originated."

Arcing occurs when an electrical current jumps between two wires or a wire and another surface. The spark can ignite.

The board, which does not determine liability or assign blame, said its probe had cost C$57 million ($39 million) and was the most complex investigation it had ever undertaken.

In the flight's final moments, the pilots reported smoke in the cockpit and dumped fuel before trying to reach Halifax for an emergency landing, 53 minutes after departure.

The fire started in a hidden area above the cockpit ceiling when electrical wire arcing ignited the cover material, made of thermal insulation blankets, the board said.

"This set off an in-flight fire that spread and increased in intensity until it led to the loss of the aircraft and human life," the board said.

It said aircraft certification standards for material flammability at the time of the accident were "inadequate."

The plane had no smoke or fire detection devices, nor suppression equipment in the area where the fire started -- although there were no regulations at the time that called for this equipment. By the time the flight crew realized the plane was in trouble, the fire had become uncontrollable.

But the board said there was nothing the pilots could have done to prevent the crash because a number of the aircraft systems failed simultaneously.

"We have concluded that, even if the pilots could have foreseen the eventual deterioration due to the fire, because of the rapid progression of the fire, they would not have been able to complete a safe landing in Halifax," said Gerden.

The safety board, in its 338-page report, added nine safety recommendations to those in an interim report, urging tests and standards for flammability for all insulation materials on commercial jets.

It called for measures to improve cockpit voice recorders, ensuring that separate generators powered separate recorders so that at least one record would be left if one system failed.

The board had earlier recommended that airlines provide in-flight firefighting equipment and improve power supplies. It said pilots should try to land as soon as there was a sign of smoke or fire, rather than trying to dump fuel.

Families of the victims cheered the board's proposals.

"The most important part of what they've done is make recommendations about safety," said Margie Topf, who lost her older sister Nancy on Swissair Flight 111.

But the International Aviation Safety Association, headed by the widow of a Swissair 111 victim, called for an immediate investigation into the "criminally negligent homicide" of parties "implicated" in the Canadian report, including the United States Federal Aviation Administration (FAA).

"The bottom line is we've heard a lot of very good recommendations from the TSB and there's absolutely nothing in the law that obligates the FAA or any other regulatory agencies to adopt any of it," said Mark Fetherolf of Palm Beach, Florida, who lost his 16-year-old daughter Tara in the crash.

"For me, there will never be closure to this," he said.