Air France Flight 447, an Airbus A330, left Rio on Sunday at 7 p.m. local time (2200 GMT, 6 p.m. EDT) with 216 passengers and 12 crew members on board, company spokeswoman Brigitte Barrand.
About four hours later, the plane sent an automatic signal indicating electrical problems while going through strong turbulence, Air France said.
The plane "crossed through a thunderous zone with strong turbulence" at 0200 GMT Monday (10 p.m. EDT Sunday). An automatic message was received fourteen minutes later "signaling electrical circuit malfunction."
Brazil's Air Force said the last contact it had with the Air France jet was at 0136 GMT (9:30 p.m. EDT Sunday), but did not say where the plane was then.
Brazil's air force was searching near the archipelago of Fernando de Noronha, about 300 kilometers (180 miles) northeast of the coastal city of Natal, a spokesman said, speaking on condition of anonymity in keeping with department policy.
The region is about 1,500 miles northeast of Rio.
Air France-KLM CEO Pierre-Henri Gourgeon, at a news conference at Charles de Gaulle Airport north of Paris, said the pilot had 11,000 hours of flying experience, including 1,700 hours flying this aircraft. No name was released.
"We are without doubt facing an air catastrophe," Gourgeon said. "At this time, the plane's fuel reserves would not permit it to still be in flight."
He said the plane was "very far" from Brazilian coast when last contact was made, without providing details.
Aviation experts said the risk the plane was brought down by lightning was slim.
"Lightning issues have been considered since the beginning of aviation. They were far more prevalent when aircraft operated at low altitudes. They are less common now since it's easier to avoid thunderstorms," said Bill Voss, president and CEO of Flight Safety Foundation, Alexandria, Va.
He said planes have specific measures built in to help dissipate electricity along the aircraft's skin.
"I cannot recall in recent history any examples of aircraft being brought down by lightning," he told The Associated Press.
Experts said the absence of a mayday call meant something happened very quickly.
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