BBC's Lee Carter: The still don't fully understand what caused the crash

Swissair flight 111 was en route from New York's John F Kennedy Airport to Geneva. All 229 passengers and crew died when the MD-11 airplane plunged into the Atlantic Ocean.

Four months later, investigators still do not known why.

Both the cockpit voice and data recorders recovered from the ocean floor were found to have stopped working six minutes before the crash.

Theoretically, even a complete electrical failure would not have totally shutdown the MD-11. Its flight controls are hydraulic and there are rudimentary battery-powered flight instruments.

Electrical problems

From the data that is available it is thought that the pilots did not realise until too late that the plane was in serious danger.

Flight 111 crashed into the Atlantic off Peggy's Cove

According to investigators, there is little sense of urgency in cockpit conversations for at least 14 minutes after the pilots first noticed an odd odour. Published reports say they then switched off the flight recorders to isolate apparent electrical problems.

The records show that they first considered diverting the flight to land in Boston shortly after taking off from New York. But that was rejected in favour of flying further to land in Halifax, Nova Scotia.

That route was then lengthened by a decision to circle back out to the sea to dump fuel. Aviation experts now say that if the pilots had landed in Boston the accident could have been averted.

Investigators are focusing on an additional in-flight gambling and entertainment system installed for its first-class passengers.

It may be the only electrical power on the plane not shutdown, and wiring linking it to the cockpit shows signs of shorting out and charring.