An Air France jet carrying 228 people from Rio de Janeiro to Paris lost contact with air traffic controllers after flying into a strong thunderstorm over the Atlantic Ocean and signaling it had an electric problem.
Chief Air France spokesman Francois Brousse said "it is possible" the plane was hit by lightning.
Air France Flight 447, an Airbus A330, was carrying 216 passengers and 12 crew members, company spokeswoman Brigitte Barrand said.
The flight left Rio on Sunday at 7 p.m. local time. About four hours later, the plane sent an automatic signal indicating electrical problems while going through strong turbulence, Air France said.
The plane disappeared about 190 miles northeast of the coastal Brazilian city of Natal, near the archipelago of Fernando de Noronha, a Brazilian air force spokesman said. The air force began a search Monday morning near Fernando de Noronha, he added, speaking on condition of anonymity in keeping with air force policy.