PARIS, June 1 -- An Air France jetliner carrying 216 passengers and a crew of 12 disappeared from radar screens during a high-altitude thunderstorm Monday on a flight from Rio de Janeiro to Paris, raising fears it had plunged into the Atlantic Ocean, French authorities said.

The Brazilian Air Force mounted a search operation off Brazil's northeast coast, near the distant Fernando de Noronha islands, according to news agency reports from Rio. But Douglas Ferreira, head of the investigation division of Brazil's Civil Aeronautics Agency, warned reporters that the search could take a long time because it was taking place in a vast stretch of open sea.

"We can fear the worst," said Jean-Louis Borloo, the French minister of ecology, who was overseeing rescue efforts from the Paris end.

Borloo said the possibility of a terrorist attack had been eliminated and officials had tentatively concluded that the plane's disappearance was due to an accident.

Shortly before disappearing, the aircraft was passing through a turbulent zone with thunder and lightning, and it sent an automatic message indicating an electrical circuit malfunction, Air France said in a communique. Air France spokesman Francois Brousse said the most probable explanation was that the plane was hit by lightning.

But outside experts said there were too few details available in the hours after the plane vanished to speculate on a cause. Planes typically fly at high enough altitudes to soar above thunderstorms, or can easily fly around them, said William R. Voss, president of the Flight Safety Foundation.

At the same time, aircraft are engineered to accept a lightning strike without serious damage. It's not unusual for an aircraft to be struck by lightning and have no damage or perhaps be left with a hole the size of a quarter on a wingtip or tail point.

"At this point there is nothing to explain why this occurred," Voss said. "There are thousands of events where aircraft are hit by lightning. I don't know of a crash caused by lightning in recent memory."

The twin-engine plane was last in contact about 4:20 a.m. Paris time as it flew 190 miles northeast of the Brazilian city of Natal and 1,500 miles northeast of its departure point at Rio, authorities in Brazil said.

The plane, Air France Flight 447, is an Airbus A330-200 long-range, medium-sized passenger jet. It was put into service with Air France in 2005 and, Air France officials said, underwent a routine inspection in April during which no anomalies were discovered.

The flight was due to land at 11:15 a.m. Paris time (5:15 a.m. EDT) at Charles de Gaulle Airport on the outskirts of the French capital. But it dropped off the radar screens over the Atlantic hours earlier, reports here said. Air France officials said they maintained hope that the plane had suffered only an outage of its transponder and radio equipment and would eventually show up again on the radar. But as time went by, they were forced to conclude that it had gone down into the sea.

"Air France regrets to announce that it is without news of Flight AF447, flying from Rio to Paris with 216 passengers on board, and it shares the emotion and worry of the families concerned," said an announcement from Air France relayed by the French news agency Agence France-Presse.

President Nicolas Sarkozy, expressing "very vivid concern," dispatched Borloo and the junior minister for transport, Dominique Bussereau, to the airport to supervise government efforts to locate the aircraft and find out what happened to the passengers, Sarkozy's office announced.

A room at the airport was set aside for families who came to greet their loved ones and a special telephone number was set up to respond to inquires, airport authorities said.

Staff writer Sholnn Freeman contributed to this report.

www.washingtonpost.com/wp-dyn/content/article/2009/06/01/AR2009060100673_pf.html