AF447: what the experts are saying

Brazilian air force search teams reported sighting wreckage in the Atlantic Ocean 400 miles northeast of Brazil's Fernando de Noronha island on Tuesday morning. The debris includes metallic fragments, kerosene and what might be a plane seat, but it is far too early to say whether it belongs to Air France flight 447, which disappeared over the Atlantic early on Monday en route from Rio de Janeiro to Paris.

Indeed, it is possible that what happened to the airliner will always remain a mystery, with the black box recorder sitting at the bottom of the ocean, never to be found.

The only concrete clues so far as to what happened to the Airbus A330-200, which had 228 passengers and crew on board, are contained in a dozen automated technical messages to Air France's operations department. The messages, which began when the plane was four hours into its 11-hour flight and heading for a storm, came over a period of about 15 minutes. They told Air France that several electrical systems had broken down.

As a result, in the absence of any evidence of a hijack or terrorism, Air France has to assume that the plane was struck by lightning. But experts generally agree that lightning alone would not have caused a fatal accident.

French and Brazilian military aircraft and warships are continuing their search over a vast area of the Atlantic between Brazil, Senegal and the Cape Verde and Canary islands. But French President Nicolas Sarkozy, who yesterday visited Charles de Gaulle airport where the flight had been due to arrive at 11.15 am local time, told relatives and friends that the chances of finding survivors were "very small".

If no survivors are found, it will be Air France's worst ever accident. The last was in July 2000 when a Concorde bound for New York crashed 60 seconds after taking off from Charles de Gaulle. All 109 people on board were killed.

WHAT THE EXPERTS ARE SAYING

• Pierre Sparaco of the French Air and Space Academy: "Lightning alone is not enough to explain it. There must be a missing link. Accident investigators talk always of a sequence of catastrophic events, and 'sequence' is the key word."

• Air Force spokesman Col Jorge Amaral: "The search is continuing because [the debris already sighted] is very little material in relation to the size [of the Airbus A330]... The command centre needs to have at least one piece of the debris with a serial number to confirm that it belongs to the airplane."

• David Learmount of Flight International magazine: "Modern aircraft are so reliable and have so many backups for every system that a single electrical fault, or even the loss of an entire circuit, would be easily dealt with - if that were all that occurred... If the last message from the plane has been correctly interpreted as a short circuit, that raises the spectre of an electrically caused fire, and fire is always serious in an aircraft."

• Douglas Ferreira Machado, head of investigation for Brazil's Civil Aeronautics Agency: "It could be a long, sad story. The black box will be at the bottom of the sea."

• Henry Margusity, senior meteorologist for AccuWeather.com: "Tropical thunderstorms tower so high that it can be impossible to fly over them. At the altitude it was flying, it's possible that the Air France plane flew directly into the most charged part of the storm."