Fifty-two minutes after leaving New York, the pilots of Swissair Flight 111 noticed an unusual smell in the cockpit. It was the evening of 2 September 1998, the MD-11 was cruising at 33,000 feet over the Atlantic south of Nova Scotia, and nothing else seemed wrong. Within minutes there was visible smoke. Twenty-one minutes after that first smell, at 22:31 local time, the aircraft hit the sea off Peggys Cove at around 300 knots.

All 229 people on board were killed. It took Canadian investigators more than four years, 98% of the wreckage and around two million recovered pieces to explain why. The answer, a fire hidden above the cockpit ceiling, fed by insulation that should never have burned, changed how every airliner is built.

Smoke in the Cockpit

Flight 111 left JFK at 20:18 New York time, bound for Geneva with 215 passengers, among them the AIDS researchers Jonathan Mann and Mary Lou Clements-Mann. Near Yarmouth, Nova Scotia, the crew detected an odour that seemed to come from the air-conditioning system. At 22:14 Atlantic time, with smoke now visible, the captain called Moncton Centre.

The crew first asked for Boston. The controller offered Halifax, which was much closer, and they accepted. But the jet was high and heavy with fuel for the Atlantic crossing. At 22:18, handed over to Halifax, it was at 21,000 feet and 30 nautical miles from the airport, too high and too close to land straight in. The crew was vectored over the sea to dump fuel while working through the checklist for smoke of unknown origin.

One step on that checklist was to switch off the "CABIN BUS" power. The crew did not know that the in-flight entertainment system was powered from a different bus, which stayed live. Worse, according to the investigation, shutting off the cabin power changed the airflow in the ventilation ducts in a way that increased the smoke in the cockpit. The fire, meanwhile, was spreading unseen in the space above the ceiling.

Mentour Pilot's full analysis of Swissair 111, from the first smell to the final minutes.

The Last Minutes

The fire began to destroy the aircraft's systems. At 22:24:28 the crew reported that they now had to fly manually, and ten seconds later declared an emergency. It was the last transmission received. At 22:25:41, both flight recorders stopped. For the final six minutes of the flight, there is no voice or data record at all, and investigators had to rebuild what happened from the wreckage.

What they found was harrowing. The heat above the cockpit was intense enough to melt aluminium parts of the ceiling structure. About a minute before impact, the first officer shut down engine number two. At 22:31:18, the MD-11 struck the sea off Peggys Cove at around 300 knots, 20 degrees nose-down and in a steep bank, with forces estimated at 350 g.

CBC's The Fifth Estate on the untold story of Swissair 111 and the investigation that followed.

Two Million Pieces

The recovery, Operation Persistence, went on until December 1999. Divers and dredges brought up about 98% of the aircraft, some 127,000 kg of debris in around two million pieces. Investigators rebuilt the forward fuselage on a frame to trace the fire's path through the wiring and insulation.

The Transportation Safety Board of Canada found that the fire most likely started with arcing in wiring connected to the in-flight entertainment network (IFEN) above the cockpit. The system ran on Windows NT and had been fitted to Swissair's MD-11s in 1997 and 1998, with seat-back touchscreens in first and business class. The arc ignited metallised polyethylene terephthalate (MPET) insulation blankets, and the fire spread from there. Circuit breakers of the time were not designed to trip on this kind of arcing.

What Changed

The TSB listed eleven causes and contributing factors and made recommendations on material flammability testing, wiring and circuit protection, flight recorder power, fire detection and fighting, and checklists. They fed into new FAA standards on aircraft wiring and fire hardening. MPET insulation, approved at the time, became a symbol of how certification had missed the danger of materials that burned once lit.

Swissair renumbered its New York to Geneva flight from SR111 to SR139. Three years later, in the autumn of 2001, the airline itself collapsed. Its successor, Swiss International Air Lines, retired the MD-11 in 2004.

Mayday: Air Disaster reconstructs the last minutes of Swissair 111.

Peggys Cove Remembers

Two memorials now stand near the crash site: one at the Whalesback, near Peggys Cove, and a larger one at Bayswater Beach on the Aspotogan Peninsula, where unidentified remains are buried.

For Switzerland, Flight 111 was a national trauma: the pride of its flag carrier, lost with everyone on board. For the rest of the industry, it was a lesson that the most dangerous fire is the one nobody can see.

Sources: Wikipedia (Swissair Flight 111), Transportation Safety Board of Canada final report A98H0003 (as cited), CTV News (ATC transcript), CBC, aeroTELEGRAPH