All 229 passengers and crew on the flight from New York to Geneva perished. Investigations showed that the cockpit voice and data recorders had stopped working six minutes before the crash.
It is thought the pilots did not realise until too late that the plane was in serious danger. There is little urgency in their voices for at least 14 minutes after they first reported noticing an odd smell.
They first considered diverting the flight to Boston but then decided to land in Halifax, Nova Scotia, instead. The route was then lengthened by a decision to circle back out to the sea to dump fuel. Aviation experts now say that if they had landed in Boston the disaster might have been averted.
Investigators are focusing on an in-flight entertainment system for passengers in first class, which might have been the only electrical power not shut down. Wiring linking it to the cockpit shows signs of shorting out and charring.