The disappearance of an Air France jet en route from Rio de Janeiro, Brazil, to Paris has left seasoned crash investigators with very little data to plumb the mystery and stricken relatives with no answers.
All 228 people aboard are feared dead. The Airbus A330-200 is believed to have vanished in a towering thunderstorm Sunday with no word from its pilots that they were in crisis.
The plane had beamed out several signals that its electrical systems had malfunctioned and had lost cabin pressure. The signals were sent not as distress calls, however, but as automated reports to Air France's maintenance system.
As a search for wreckage began over a vast swath of ocean between Brazil and the African coast, experts struggled to offer plausible theories as to how a well-maintained modern jetliner, built to withstand electrical and physical buffeting far greater than nature usually offers, could have gone down so silently and mysteriously.
There were no suggestions Monday that a bomb, hijacking or sabotage was to blame. Whatever of the plane's final minutes was recorded in its black box may never be known, because it is presumably at the bottom of the Atlantic.
Pilots flying a Brazilian commercial jet spotted what they thought was fire in the ocean along the Air France jet's route early Monday, before they knew of the disappearance, the TAM airline said. The Brazilian air force was investigating.
As is common with trans-ocean flights, the plane was too far out over the sea to be tracked on land-based radar.
Stricken relatives descended on Terminal 2D at Charles de Gaulle airport in Paris, where the airline established a crisis center Monday. French President Nicolas Sarkozy offered no hope to the families.
The search is daunting. Brazilian officials said the area where they think the jet went down is so remote the first military boats will not arrive there until Wednesday morning. Air force jets from France and Brazil were crisscrossing the ocean Monday.
Air traffic controllers lost contact with Air France Flight 447 just as the jet was entering a band of violent thunderstorms and heavy turbulence that stretched along the equator.
Experts were at a loss to explain fatal damage from lightning or a tropical storm, both of which jetliners face routinely.
Brigitte Barrand, an Air France spokeswoman, said the highly experienced pilot had clocked 11,000 flying hours, including 1,100 hours on Airbus 330 jets. No Airbus 330-200 passenger flight had ever been involved in a fatal crash, according to the Aviation Safety Network.
"A completely unexpected situation occurred on board the aircraft," said Pierre-Henri Gourgeon, the chief executive of Air France-KLM. "Lightning alone is not enough to explain the loss of this plane and turbulence alone is not enough."
If no survivors are found, it will be the worst air disaster since 2001. Two Americans were among those on board.