From the water and from the air, teams are converging on the debris field, located some 400 miles from the Brazilian islands of Fernando de Noronha.
Ten planes from Brazil, three from France and one from the United States are hoping to soon gather clues about what caused the plane to disappear en route from Rio de Janeiro to Paris. Four ships have also changed their routes to get close to the area of the sea where remnants, including what appeared to be airplane seats, were spotted about 630 miles northeast of Brazil's coast.
According to the Brazilian air force, there are no indications of survivors.
"Because of the way this airplane disappeared, we have very little evidence to start to put together what happened," said John Hansman, a professor of aeronautics and astronautics at Massachusetts Institute of Technology. "So anything they can get from the debris field in the ocean is going to be important in terms of clues."
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The missing Airbus A330 had 228 people onboard when it departed Sunday night.
A U.S. maritime surveillance aircraft has been dispatched to Brazil from El Salvador to assist in the search, ABC News has been told. Tonight in France, French Transport Minister Jean-Louis Borloo also gave instructions for a search and exploration ship to be sent to the crash site.
The French ship is equipped with tools to help recover debris, including an underwater robots that can plunge about 20,000 feet underwater. It could be a few days before the ship arrives where the debris has been spotted.
What made the plane disappear is not clear, although it did enter an area with severe thunderstorm activity about the time it vanished.
ABC News has confirmed that two commercial planes flew virtually the same route as that taken by the Air France jet just before and after the missing flight.
A Lufthansa spokesman told ABC News he knew of one flight in the area at the time, but it is not clear if that plane encounterted any poor weather.
"This flight operated normally without any irregularities reported by the crew," Lufthansa said in a Tuesday statement.
Overnight word also came that a crew from TAM, Brazil's largest air carrier, saw orange spots on the ocean while flying over the same general area as the Air France Flight 447.
But crew on a French merchant ship nearby, the Douce France, said they found no trace of wreckage or survivors after searching the area, the Brazilian Air Force said today in a statement.
"If that was, in fact, debris burning from this aircraft, then that tells us that it broke up in flight," ABC News aviation consultant John Nance said today.
Mystery Over the Atlantic: The Passengers Onboard
Meanwhile, the list of the missing indicates a virtual United Nations of passengers: Those onboard the plane came from more than 30 countries, including Americans Michael and Ann Harris, who had been living in Rio for more than a year. This afternoon, U.S. State department officials said a third American, a dual citizen traveling under a foreign passport, was also onboard.
Earlier today, Commander Prazuck, a spokesman for the French military joint staff, told the BBC Radio 4 Today program, it was "very unlikely" that any survivors would be found, echoing the words of his president, Nicolas Sarkozy, who said Monday that he had told family members of passengers to prepare for the worst.
If there are no survivors, as is feared, it would be one of the world's worst aviation disasters since 2001.
The passengers include three U.S. citizens, 61 French citizens, 58 Brazilians, 26 Germans, nine Chinese and nine Italians. Hope is now almost gone for the passengers and crew, which include seven children, a baby, 126 men and 82 women.
Michael Harris is a geologist working in Brazil for Devon Energy, a natural gas and oil producer. He'd been transferred from Houston to Brazil in 2008.
"We are extremely saddened by this development and trying to monitor the situation as it unfolds," said Devon Energy spokesman Tony Thornton in a statement. "We're doing what we can to help the family at this time."
U.S. State Department spokesman Robert Wood has said the U.S. government is also in touch with the families of the Americans onboard.
All 12 members of the crew on the plane were French, according to the airline.
Finding bodies, survivors or significant pieces of the debris such as flight data recorders, in water Google Earth estimates to be 13,000 feet deep, could be daunting.
"The mid-oceans are one of the remotest parts of the world," Hansman said. "It's like going to the North Pole. It's in an area where there is very limited ability to communicate."
So far, the best clues as to what happened so far come from the plane's own computers, which sent 10 automatic messages to Air France maintenance indicating a problem, including some sort of electrical failure, before the plane disappeared.
"It's giving you a little bit of a breadcrumb history of what was happening on the airplane somewhere in the final few minutes of its flight," Hansman said.
Air France says the communications came just 14 minutes after the Airbus A330 hit turbulence. The jet may have been navigating a stormy area around the equator known as the intertropical convergence zone.
Borloo said he did not think bad weather alone could have brought the plane down. Officials "do not believe a simple bolt of lightning, something relatively classic in aviation could have caused the loss of the craft," Borloo said, according to The Associated Press. He also brushed off the idea that terrrorism or a hijacking could be involved.
He also told France's RTV radio, "There really had to be a succession of extraordinary events to be able to explain this situation."
"You never say never," he told ABC News' "Good Morning America," about the chance of lightning triggering a crash, but added that it would be almost unheard of for a plane to be downed by lightning alone.
Nance also addressed whether turbulence can break up a plane: "In most circumstances, absolutely not," he said. "The aircraft can take anything the atmosphere can throw at it except for tornadoes."
In very rare cases, Nance said, a plane could be trying to recover from severe turbulence and then hit more, causing too much stress for the plane.
Accu Weather's Ken Reeves says towering thunderstorms are common over that area of the Atlantic. He said planes typically fly at about 35,000 to 37,000 feet, and storms in the tropics can be as high as 50,000 feet.
"In that part of the tropics, with as high as the thunderstorms are, it can be difficult having to go hundreds and hundreds of miles out of your way in order to just get to the point you're trying to get to," Reeves said.
"We are really talking about extreme circumstances here," said William Voss, president and CEO of Flight Safety Foundation. "And so a rainy night out of LaGuardia isn't what we are talking about. We are talking about situations that are very extreme, very severe turbulence is assumed occurred here. And there's not many of us -- not even many pilots that have really experienced severe turbulence. You would know it if you had."
The Airbus jet, only four years old, did have sophisticated radar that should have helped the pilots try to skirt any violent weather.
The Disappearance of Air France Flight 447
The flight had been expected to land in Paris at 5:15 a.m. ET. after leaving Rio around 6 p.m. Sunday night.
The head of Air France, Pierre Henri Gourgeon, told reporters the plane's last radio contact with Brazilian air control was at 9:30 p.m. ET.
Crashing nearly four hours into the flight would be highly unusual: 94 percent of crashes happen on take-off or landing.
Still, former National Transportation Safety Board investigator Greg Feith said late Monday that it was too early to jump to conclusions about what happened.
"We don't have enough information to really put a storyline together, and it may not be possible to put an accurate storyline together, especially if the flight data recorder and cockpit voice recorder are never recovered," Feith said.
If found, the plane's black boxes would also provide many more clues about what happened. Experts said the black boxes emit signals, although only for a finite period of time, in the water. With tracking beacons that activate when the boxes get wet, the back box radio signal can work for about 30 days. Search teams will have to be within 4,000 to 5,000 feet of the black box location to pick up the signals.
Lt. Col. Jed Hudson, a commander at Tyndall Air Force Base in Florida, said all planes also have emergency transmitters in their tails as well that are designed to send out a distress signal in case of emergency.
It's possible that this one either malfunctioned or there wasn't a satellite passing overhead to detect the signal at the time the plane was in trouble. The information can be stored and detected once satellites pass overhead -- unless it is too far underwater.
The Brazilian Air Force said in a statement that it had been anticipating radio contact with the plane when it was still over northeast Brazil, but when it received no radio communication, Brazilian air traffic control contacted air traffic control in Dakar, Senegal. There was no Mayday call and no nearby planes received a call for help on the international emergency frequency.
Air France said the captain of the flight had more than 11,000 hours of flight time, including 1,700 hours on A330/A340.
There are 341 A330 planes of this type operating worldwide. The plane's manufacturer, Airbus, released a statement saying it would be "inappropriate for Airbus to enter into any form of speculation into the causes of the accident.
"The concerns and sympathy of the Airbus employees go to the families, friends and loved ones affected by the accident," the statement read.
ABC News' Luis Martinez, Christel Kucharz, Sonia Gallego, Gabriel O'Rorke, Christophe Schpoliansky, Phoebe Natanson, Samira Parkinson-Smith, and Kirit Radia, Reuters and The Associated Press contributed to this report.