An electrical short circuit, probably in the wiring of an in-flight entertainment system, triggered the roaring fire that brought down Swissair Flight 111 41/2 years ago off the coast of Nova Scotia, the Transportation Safety Board of Canada said yesterday in issuing its final report on the crash.

All 229 people aboard died when the McDonnell Douglas MD-11 crashed Sept. 2, 1998, into the Atlantic Ocean near the hamlet of Peggy's Cove, about 20 minutes after the pilots reported an odd odor and smoke in the cockpit. The investigation was the largest and most complicated in Canadian history, partly because all communication was lost with the aircraft and neither on-board recorder worked for the last 51/2 minutes of the flight.

The board's in-depth analysis concluded that the fire raced so quickly through the flammable insulation that even if the pilots had taken immediate action to land at Halifax after they detected the odor, "it would have been impossible for the pilots to continue maintaining control of the aircraft for the amount of time necessary to reach the airport and complete a safe landing." At the time, there was speculation that the pilots could have saved the plane with an immediate emergency landing, rather than taking time to dump fuel and prepare the cabin for landing.

Although the plane's cockpit filled with smoke and noxious fumes, the passengers and crew were killed by the aircraft's impact with the water at an estimated speed of almost 300 knots, about 345 mph, the board said. The board found no heat damage to any of the recovered remains or evidence of major heat damage in the cockpit.

The final report confirmed preliminary findings that have already resulted in major changes to MD-11s and some Boeing 747s and set new industrywide standards. The metalized Mylar insulation used in the MD-11 has long since been removed and can no longer be used on aircraft. The in-flight entertainment system, a product of the defunct company In Flight Technologies, has been removed from all aircraft and banned from future use. Numerous changes have been ordered in other in-flight entertainment systems.

The board also made several other recommendations involving aircraft electrical systems, certification of add-on systems such as the entertainment system, and improvements to protect information on cockpit voice recorders and flight data recorders.

It determined that the fire "most likely" started near an area of melted copper that indicated electrical arcing in the power supply cable to the in-flight entertainment system. "This arc was likely associated with the fire-initiating event," the report said. "However, it could not be determined whether the arced wire was the lead event."

Once the fire started, routine trouble-shooting by the crew, which turned off a cabin air circulation system, had the unintended effect of allowing smoke and smoldering fire in the forward ceiling to move toward the cockpit.

Worse, end caps on air conditioning ducts burned off and blew a supply of oxygen-rich air into the ceiling, fanning the flames. It is even possible, the board said, that the fire breached the supply line to the pilot's oxygen system, spewing pure oxygen on the fire.

The report did help to clear up some of the crash's enduring mysteries, including why the crew did not think anything serious was happening until just a second before both pilots, at the same moment, suddenly declared an emergency.

The report said that the ceiling fire "would initially generate a small creeping flame that would produce a small amount of smoke with a relatively strong accompanying odor." Rather than coming through the ceiling, the odor and smoke would follow a "corkscrew path" and would "initially present a weak visual indication" to the pilots. The pilots thought at first that there was a problem with the air conditioning system, a relatively routine event.

The gradual buildup of heat in electrical components and behind circuit breaker panels then caused aircraft systems, one by one, to malfunction. That eventually included primary pilot flight displays.

In the end, the board said, the fire would have broken into the cockpit suddenly with huge amounts of smoke and gases. Melted portions of the cockpit ceiling liner fell out, leaving burn marks in the carpet, and drops of molten aluminum fell onto the right cockpit observer's seat.

Most of the falling ceiling liner and the smoke and burning material would have blown into the left side of the cockpit, where the captain sits. The captain's seat was found pushed back from the controls, while the first officer's chair was found in its normal position.

There was no evidence that the passengers were being prepared for a ditching at sea, the board said. However, the body of a professional pilot traveling as a passenger was clad in a life vest, indicating that at least he knew the plane was going down over the ocean.

Vic Gerden of the Transportation Safety Board of Canada holds flammable insulation at a news conference.