Government and airline officials played down the likelihood of a bomb yesterday. Engine failure seems unlikely, as witnesses heard the roar of jets shortly before the crash. The only clue is that the crew reported smoke in the cockpit.
Problems began when the plane had reached it cruising altitude of 33,000 feet, an hour after leaving New York. The pilots began dumping fuel but were unable to control the plane. Key questions should be quickly answered by the plane's "black boxes". The aircraft had two, the cockpit voice recorder and flight data recorder - both designed to resist any crash impact. They also have radio signalling devices.
Ten investigators from the Canadian Transportation Safety Board have arrived in Nova Scotia and are being joined by US and Swiss experts.
First the team will send divers to recover the boxes. "Black boxes have been recovered from much deeper water," said David Learmount, operations and safety editor of Flight International.
He pointed out that European safety regulations require airlines to make their black boxes record much more in-flight information than American regulators. "That's why we don't know what happened to TWA 800," Mr Learmount said. TWA 800 exploded off the American coast in 1996, killing 230. "TWA 800 was a very elderly 747, over 20 years old, but this aircraft is relatively young, with the latest equipment. It had a digital cockpit and there will be large amounts of information." He also cited two other fatal accidents involving US passenger aircraft, in Pittsburgh and Colorado Springs in 1994, for which the cause is unknown due to lack of black-box information.
In a European aircraft the black boxes will have recorded at least 200 pieces of information, enabling investigators to establish, for instance, whether there was a fire on board, or in an engine, or if a part failed. What the cockpit crew said in the minutes leading up to the crash will also be revealing. The aircraft was an MD-11, a wide-body three-engined jet. It is the successor of the DC-10, the McDonnell Douglas jumbo that acquired a reputation as a death-trap after a series of accidents in the 1970s. The MD-11's designation hides its relationship with the DC-10.
"There has never been an accident involving the MD-11 in which there was anything wrong with the aircraft," Mr Learmount said. "The MD-11 has an impeccable safety record."
Swissair SR111 was a scheduled flight from New York to Geneva. It was about an hour out, having passed Boston, when some kind of problem occurred. The cockpit crew radioed that they were going to make an emergency landing. They then reported smoke in the cabin and said they were going to try to land at Halifax international airport, directly on their path.
Unlike TWA 800, which was subject to an explosion, flight SR111 seems to have been suffering a developing problem. Shortly before it crashed the crew had given the message "Pan, pan, pan", indicating something was seriously wrong. They were 30 miles from Halifax airport's runway.
Mr Learmount said it was hard to reach any conclusions at the moment. "We don't know what the pilot was doing. We don't know what caused the smoke. We don't know if the pilot was in control of the aircraft when it came down or if he intended to ditch."
Smoke in the cockpit is not in itself an insurmountable problem. The crew have masks and goggles and can still land an aircraft.
But they would be concerned about the passengers: smoke in aircraft is highly toxic and potentially fatal for passengers not supplied with smoke masks.
Swissair's last serious accident was 20 years ago, when 14 people died when a DC-8 overshot the runway at Athens. In 1970 a plane was destroyed by a bomb.
But one has to go back to 3 September 1963 to find an accident of similar proportions: a Caravelle crashed near Zurich, killing all 80 people on board.Reuse content