On 2 September 1998, Swissair flight 111 left New York for Geneva. Just under an hour later the crew smelled smoke. Fifty-one minutes after that first indication, the McDonnell Douglas MD-11 struck the Atlantic near Peggy's Cove, Nova Scotia. All 229 people aboard died.
The fire
The source was electrical arcing in wiring above the cockpit ceiling, in the area serving a newly installed in-flight entertainment system. That system had been added to the aircraft under a supplemental type certificate — an approval process for modifications separate from the original aircraft certification.
The arcing ignited flammable material in the ceiling. The critical finding was about the insulation: the MD-11's thermal acoustic insulation used a metallised polyethylene terephthalate covering that, contrary to what the certification test had suggested, would propagate flame. Once alight, it carried fire along the ceiling above the cockpit and forward cabin, out of sight and out of reach.
The decision to divert
The crew smelled an unusual odour and initially assessed it as an air conditioning issue. As it became clear it was smoke, they declared an emergency and diverted towards Halifax.
They were high and close, and to land they needed to lose altitude and dump fuel — the aircraft was far above maximum landing weight. They turned out over the water to dump. During that sequence the fire destroyed enough of the aircraft's systems that the flight deck displays and then control were lost.
The investigation examined whether an immediate descent for landing, without the fuel dump, would have changed the outcome. The TSB concluded the fire had progressed further than the crew could have known from the flight deck — an in-flight fire above the ceiling gives almost no information about how bad it is until it is too late. It did not fault the crew's decision, and it recommended that checklists treat smoke of unknown origin as a reason to land immediately rather than to diagnose first.
The investigation
Canada's Transportation Safety Board ran what became the largest and most expensive investigation in its history, lasting four and a half years. More than 98% of the aircraft was recovered from the seabed, and roughly two million fragments were brought up and reassembled in a hangar in Shearwater. Investigators mapped the fire's progression through the wreckage.
The recovery effort involved the Canadian Navy, the Coast Guard and the fishing community of the South Shore, and it left a lasting mark on the region. Memorials stand at Peggy's Cove and Bayswater.
What changed
The findings had global effect. The metallised insulation implicated in the fire was banned and required to be removed from thousands of aircraft worldwide — an enormous retrofit programme. Flammability test standards for cabin materials were made significantly more demanding, because the existing test had passed a material that in reality spread fire.
Oversight of supplemental type certificates was tightened, addressing how a modification could be installed without full assessment of its interaction with existing systems. And smoke and fire checklists across the industry were rewritten around a principle the TSB stated plainly: with an in-flight fire you cannot see, time spent diagnosing is time you may not have.