The disappearance of an Air France jet en route from Rio de Janeiro to Paris on Sunday evening left seasoned crash investigators with a mystery to plumb and very little data to work with.

The Airbus A330-200, carrying 228 passengers and crew members, is believed to have vanished in a towering thunderstorm 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, according to one report, that it had lost cabin pressure. The signals were sent not as distress calls, however, but as automated reports to Air France’s maintenance system, and were not read for hours, until air traffic controllers realized that the plane’s crew had not radioed in on schedule.

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 on Monday that a bomb, a 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. As is common with trans-ocean flights, it was too far out over the sea to be tracked on land-based radar from Brazil or Senegal. Whether its location was captured by satellite or other planes’ radar is not known yet.

The plane, Flight AF 447, was scheduled to arrive at Charles de Gaulle airport at 11:10 a.m. local time. Stricken relatives descended on Terminal 2D, where the airline established a crisis center. A black-robed priest was making his way past hordes of police officers and journalists to comfort relatives of those on the flight.

“Air France is extremely distraught, and the whole team of Air France is suffering,” Pierre-Henri Gourgeon, the chief executive of Air France-KLM, told reporters in Paris. “We would like to say to the relatives of the victims that we are totally with them and will make every effort to help them.”

Image Relatives and friends of Air France flight AF447 passengers were sent to Windsor Hotel in Rio de Janeiro on Monday to wait for more information. Credit... Bruno Domingos/Reuters

President Nicolas Sarkozy of France said: “It’s a tragic accident. The chances of finding survivors are tiny.”

There were people of 32 nationalities aboard, including 58 Brazilians, 61 French and 2 Americans, Air France said in a statement based on information from Brazilian authorities.

The flight took off from Rio de Janeiro at 7:30 p.m. local time (6:30 p.m. Eastern time), and its last verbal communication with air traffic control was three hours later, at 10:33, according to a statement from Brazil’s civil aviation agency. At that time, the flight was at 35,000 feet and traveling at 520 miles per hour.

About a half-hour later, it apparently encountered an electrical storm with “very heavy turbulence,” Air France said. The last communication from it came at 11:14  a series of automatic messages indicating it had suffered an electrical-system malfunction. The Associated Press reported that it also suffered a loss of cabin pressure.

Brazilian officials said the plane disappeared over the Atlantic somewhere between a point 186 miles northeast of their coastal city Natal and the Cape Verde islands off Africa. The area is known as the intertropical convergence zone, where the tropics of the Northern and Southern Hemispheres mix, sometimes creating violent and unpredictable thunderstorms that can rise to 55,000 feet, higher than commercial jetliners can go.

Experts were at a loss to explain fatal damage from lightning or a tropical storm, both of which jetliners face routinely, despite efforts to avoid them  as much out of concern for passengers’ nerves as for the planes’ safety.

Pilots are trained to go over or around thunderstorms rather than through them. 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.

“A completely unexpected situation occurred on board the aircraft,” Mr. Gourgeon told France’s LCI television.