Heavy seas and low cloud today hampered the search for the wreckage of the Air France jet that crashed into the Atlantic with 228 people on board.
Aircraft and ships were looking at a vast zone extending from far off north-east Brazil to waters off West Africa.
So far have no signs of the four-year-old Airbus have been found.
Investigators on both sides of the ocean worked through the night to try to discover what downed it – wind and hail from towering thunderstorms, lightning, or a catastrophic combination of factors.
But they were unable to come to any conclusions, saying recovery of the plane’s two black box flight recorders was essential in finding out what happened to it. They will broadcast locating radio signals from internal power for up to 30 days.
French defense minister Herve Morin said there were “no signs so far” that terrorism was involved, but added that “all hypotheses must be studied”.
The French military said bad weather made the search difficult with search planes being forced to fly very low over the water, limiting their line of sight.
“For the time being we can’t find anything,” said a spokesman. “There are a lot of squalls, a lot of storms.”
Even once debris is found, the rescuers’ work will be arduous.
“The research area overhangs an underwater mountain range as big as the Andes. The underwater landscape is very steep,” the spokesman said.
France’s junior transport minister Dominique Bussereau predicted a “very long investigation, it could be several days, several weeks, or several months”.
French police were studying passenger lists and maintenance records, and preparing to take DNA from passengers’ relatives to help identify any bodies. If there are no survivors, as feared, it would be the world’s worst aviation disaster since 2001.
Brazil’s largest airline, TAM, said its pilots flying from Paris to Rio spotted what they thought was fire in the ocean along the Air France jet’s route. But Brazil’s air force said a French merchant ship searched that area “without identifying any trace of the flight.”
Two Brazilian air force jets conducted night searches over the Atlantic early today , joining other Brazilian aircraft, including two helicopters. The first of three Brazilian ships was expected to arrive in the remote area tomorrow.
With nothing more to go on than the last point where Flight 447 from Rio to Paris made contact – about 745 miles north-east of the Brazilian coastal city of Natal – search teams faced an immense area of open ocean, with depths as much as 15,000 feet.
The Airbus A330-200 was cruising normally at 35,000 feet and 522 mph 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 lay a line of towering thunderstorms. Bands of extremely turbulent weather stretched across the Atlantic toward Africa.
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.