RIO DE JANEIRO -- Searchers raced against the clock Tuesday to find wreckage of Air France Flight 447, which disappeared in the Atlantic Ocean with 228 people aboard. French investigators said a series of extraordinary events likely brought the airliner down.
Rescuers scanning deep waters in a vast zone extending far off northeast Brazil toward West Africa have not turned up confirmed signs of the plane, or any survivors. The 4-year-old Airbus jet was last heard from at 0214 GMT Monday en route from Rio de Janeiro to Paris.
Investigators on both sides of the ocean worked through the night to determine what brought it down _ wind and hail from towering thunderheads, lightning, or a catastrophic combination of factors.
The French government minister overseeing transportation, Jean-Louis Borloo, said French police were studying passenger lists.
He also said officials "do not believe that a simple bolt of lightning, something relatively classic in aviation, could have caused the loss of the craft."
"There really had to be a succession of extraordinary events to be able to explain this situation," Borloo said on RTL radio Tuesday.
"The race against the clock has begun" to find the plane's two black boxes, which emit signals up to 30 days, he said. He said they were likely in very deep waters.
The chance of finding survivors at this point, he said, "is very very small, even nonexistent."
Brazil's largest airline, TAM, released a statement late Monday saying that pilots flying one of its commercial flights from Paris to Rio spotted what they thought was fire in the ocean along the Air France jet's route.
Air Force spokesman Col. Jorge Amaral told the Agencia Brasil official news service that authorities were investigating the report.
"There is information that the pilot of a TAM aircraft saw several orange points on the ocean while flying over the region," he said.
But Brazil's air force said in a Tuesday statement that a French merchant ship _ the Douce France _ had conducted a search of the area where TAM reported seeing fire "without identifying any trace of the flight."
Air France spokesman Nicolas Petteau said Tuesday that the airline had no information about any sighting of a fire or debris.
France's Defense Minister Herve Morin said "we have no signs so far" indicating terrorism was involved. Still, he added on French radio, "All hypotheses must be studied."
Two Brazilian air force jets conducted night searches over the Atlantic early Tuesday. Six Brazilian aircraft, including two helicopters, were involved in the search, authorities said. The first of three Brazilian ships was expected to arrive in the remote area Wednesday.
Authorities have asked any commercial vessels in the area to aid in the search and France sought U.S. satellite help to find the wreckage.President Barack Obama told French television stations Canal-Plus and i-Tele that the United States was ready to do everything necessary to find out what happened to the missing plane.
A French search plane took off from a military base in Senegal on Monday, to be joined by two more and a naval vessel.
With nothing more to go on than the last point where Flight 447 made contact _ about 745 miles (1,200 kilometers) northeast of the Brazilian coastal city of Natal _ search teams faced an immense area of open ocean, with depths as much as 15,000 feet (4,570 meters).
If there are no survivors, as feared, it would be the world's worst aviation disaster since 2001.
On board the flight were 61 French citizens, 58 Brazilians, 26 Germans, nine Chinese and nine Italians. A lesser number of citizens from 27 other countries also were on the passenger list, including two Americans.
Air France was helping relatives of the passengers at Paris' Charles de Gaulle airport, where some 40 people remained Tuesday.
Air France was also helping families in Rio. Bernardo Ciriaco, a civil servant, said he arrived at the airport in a panic because he knew his brother Gustavo was on one of two Air France flights heading to Paris on Sunday night.
About two hours later, he received a phone call from Gustavo, telling him he had landed safely in Europe.
Gustavo told him that he had been bumped to the flight that is missing but had insisted that he be allowed on the booked earlier flight and arrived safely.
"Our family is so relieved," Ciriaco said.
The Airbus A330-200 was cruising normally at 35,000 feet (10,670 meters) and 522 mph (840 kph) just before it disappeared nearly four hours into the flight. No trouble was reported as the plane left radar contact, beyond Brazil's Fernando de Noronha archipelago.
But just north of the equator, a line of towering thunderstorms loomed. Bands of extremely turbulent weather stretched across the Atlantic toward Africa, as they often do in the area this time of year.
Soon afterward, the plane sent an automatic message reporting electrical system failure and a loss of cabin pressure. Air France said the message was the last it heard from Flight 447.
Chief Air France spokesman Francois Brousse said a lightning strike could have damaged the plane.
Other pointed to turbulence as a more dangerous factor.
The plane disappeared in an area of the mid-Atlantic ocean not covered by radar. Brazilian, African, Spanish and French air traffic controllers tried in vain to establish contact.
The pilot had 11,000 hours of flying experience, including 1,700 hours flying this aircraft.
Experts said the absence of a mayday call meant something happened very quickly.
Associated Press reporters Emma Vandore, Laurent Joan-Grange in Paris; Alan Clendenning and Tales Azzoni in Sao Paulo and Marco Sibaja in Brasilia contributed to this report.