A sparking wire in the cockpit ceiling above and behind the co-pilot's head "most likely" started a creeping fire in flammable insulation that quickly crippled Swissair Flight 111 and caused it to crash off Peggys Cove in 1998, killing all 229 people on board, according to a final report issued yesterday.
"Without the presence of [the metalized insulation]and other flammable materials, this accident would not have happened," said Vic Gerden, the Transportation Safety Board's lead investigator into the worst aviation disaster ever in Canadian airspace.
Although investigators admit they can't be absolutely sure which wire arced first, they say the crash and the probe that followed it uncovered a litany of problems and have put an end to the culture of complacency in the airline industry about the catastrophic consequences of fire aboard airliners.
"It's the biggest contribution Canada has ever made to aviation safety, " said Camille Theriault, chairman of the Transportation Safety Board.
During an investigation that took 4½ years and cost $57-million, investigators pieced together nearly two million fragments from the shattered jetliner. Ever since the plane plunged into St. Margarets Bay after pilots vainly tried in horrific and worsening fire conditions to keep the stricken jetliner aloft without electrical power and with failing systems, the TSB has issued a wide-ranging call for changes in the aviation industry.
After the Swissair Flight 111 crash on Sept 2, 1998, pilots realized how serious fire can be and "diversions because of smoke have increased significantly," Mr. Gerden said in an interview. He also said the industry now appreciates the need to conduct much tougher flammability tests before certifying materials for use in aircraft.
Nine additional specific recommendations were issued yesterday, bringing to 23 the total arising out of the investigation. They range from urging regulators to make airlines teach flight and cabin crews an aggressive fire-fighting strategy to calling for emergency power sources to keep vital flight and voice recorders running.
Ever since the big, three-engined jet flying one of Swissair's premier routes crashed off the Nova Scotia coast barely 21 minutes after the co-pilot first noticed an odd odour, there has been speculation over whether the crew had time to make an emergency landing at Halifax International Airport, which lay directly ahead of them.
"We have concluded," Mr. Gerden said, that even if the pilots had fully understood the potential gravity of the situation and immediately declared an emergency and made a rapid descent, "they would not have been able to make a safe landing."
Still, as part of its investigation, the TSB calculated the flight profile and time needed to land the aircraft. That ideal, theoretical emergency descent profile begins just three seconds after the crew declared a less urgent "Pan, Pan, Pan" situation and told air-traffic controllers they wanted to divert to Boston.
They agreed to divert to Halifax after the controllers pointed out it was much nearer.
Using computer modelling and inputting the aircraft's weight and the winds at the time near Halifax, the theoretical descent would have put the aircraft on the runway 13 minutes after the initial "Pan, Pan, Pan" radio call.
"It is coincidental that the theoretical best time to initiate a descent to land in the shortest time is only a few seconds after the Pan, Pan call," the TSB reported. "It would have taken approximately 13 minutes and 8 seconds to descend from FL330 [Swissair 111's cruising altitude of 33,000 feet, or 10,000 metres]down to a landing and complete stop," the TSB said.
Instead, 13 minutes later, the Swissair pilots were heading back out toward the ocean, flying on rudimentary emergency instruments, as chunks of burning cockpit ceiling fell and smoke filled the cockpit.
Although the crew managed to keep the aircraft aloft for four minutes, Mr. Gerden said conditions were so horrific and so many systems had failed that, in his judgment, a safe landing was not possible even if an initial decision had been made for an emergency landing.
Nor could the pilots have reasonably been expected to make that decision, he said. They thought they were dealing with smoke in the air-conditioning system, and nothing in their training or their instruments suggested it might be something far more serious.
Swissair, now defunct, said the pilots couldn't have landed the plane shortly after the accident but other MD-11 pilots using simulators have managed to demonstrate successful landings in the time available. However, neither they nor the TSB investigators know exactly what systems were available to the crew near the end because both the flight and cockpit data recorders failed 5½ minutes before impact.
Although the TSB determined that the video and gambling system that Swissair had installed in its MD-11 fleet had been improperly wired to one of the aircraft's main electrical systems rather than the non-essential cabin electrics, and that the U.S. Federal Aviation Administration had failed to properly oversee that installation, the improper installation of the system didn't cause the accident.
However, one of the wires to the system has emerged as the prime suspect for the initial spark, investigators said.
Before going out of business, Swissair removed the entertainment systems soon after the accident. It also installed fire detection and suppression systems in its aircraft, a move the TSB wants to see undertaken throughout the civil aviation industry.