Searchers Find 23-Foot Piece of Airplane in Hunt for Missing Air France Flight Another Air France flight was threatened days before Flight 447 crashed.

June 3, 2009  -- The pilot of the Air France flight that disappeared over the Atlantic Ocean sent a text message to the airline saying the plane had encountered bad weather, ABC News has learned.

As investigators examine communications sent from the plane before it vanished, searchers hunting for clues on the Atlantic today found a 23-foot piece of airplane at sea, Brazilian air force spokesman Col. Jorge Amaral said.

Watch "World News with Charles Gibson" Tonight at 6:30 p.m. ET for the full report.

Several other teams of people on planes and ships are still making their way to the remote crash site with equipment to recover debris -- including a French search and exploration ship, due to arrive at the crash site Friday, equipped with robots that can plunge about 20,000 feet underwater to help recover wreckage.

That's the same team that worked with Dr. Robert Ballard to find the Titanic in the 1980s.

Ballard has a unique perspective on what lies ahead in the underwater search for missing Air France flight 447.

"Heavy objects will go to the bottom very, very rapidly," said Ballard, director of the Center for Ocean Exploration and Archeological Oceanography at the University of Rhode Island. "Lighter objects are carried for great distances, much like the lifeboats of the Titanic were miles and miles away from where we actually found the Titanic. And in many ways, the debris they're finding are like the lifeboats of the Titanic, floating on the surface, being carried further and further."

A forensic scientist is also believed to be onboard one of the planes on its way to help with the recovery operation. The U.S. Coast Guard is assisting in the effort to provide a "reverse drift" simulation, working backwards to help determine where the plane's fuselage might be based on where wreckage is floating.

Bad weather is meantime hampering recovery efforts, with sea currents said to be impeding the process. And weather aside, recovering debris in this part of the ocean may not be easy. The underwater area where the search is focused is extremely mountainous terrain, and Google Earth estimates the water there to be 13,000 feet deep.

"That's like searching for an airplane in the surface of the mountains. You could be very close and not be able to see the wreckage," said John Hansman, a professor of aeronautics and astronautics at the Massachusetts Institute of Technology.

"The terrain here is worse than the terrain where we lost the Titanic," Ballard added. "The Titanic is sort of like in the Badlands of the Dakotas compared to the Rocky Mountains."

Bomb Threat on An Air France Flight Just Days Earlier

The flight from Rio de Janeiro to Paris vanished with 228 people onboard Sunday night. On Tuesday searchers found an oil slick and debris from the plane floating in the Atlantic 700 miles off the coast of Brazil.

Today, ABC News has confirmed that Air France received a bomb threat over the phone concerning a flight from Buenos Aires, Argentina, to Paris days before Air France flight 447 disappeared over the Atlantic.

Authorities at Buenos Aires' Ezeiza Airport delayed the May 27 flight before takeoff and conducted a 90-minute search of the threatened aircraft. Passengers were not evacuated during the search, which yielded no explosive material. After the inspection, authorities allowed the plane to take off for Paris.

Four days later, flight 447 departed from Rio de Janeiro. There was no known threat against the missing flight.

Today, the head of France's accident investigation agency, Paul-Louis Arslanian, described the case of the missing flight 447 as the "worst French aviation disaster in history."

In Brazil's president, Luiz Inácio Lula da Silva, expressed his determination to find the plane.

"A country that could find oil in 3,700 meters deep in the ocean is going to be able to find a plane 1,200 meters deep," he said in a statement.

Passenger Arthur Coakley's wife keeps trying his cell phone -- also determined to get an answer.

"I haven't tried it today, but yesterday it was ringing," said Patricia Coakley. "So maybe they're not at the bottom of the sea."

Air France Flight 447: Weather Worries

The reasons behind the crash remain unclear, with many speculating that it could have been a result of thunderstorms and lightning or a combination of both. The four-year-old Airbus jet did have sophisticated radar that should have helped the pilots try to skirt any violent weather.

Arslanian said that to the best of his knowledge, the pilot at the controls told Brazilian air control that he was experiencing turbulence about 30 minutes before the plane's disappearance. He said it was unclear whether the chief pilot was in the cockpit when the plane went down, since pilots usually take turns at the controls during long flights.

He stressed that the investigation was only in its early stages, and he could not confirm how the plane went down.

"We don't even know the exact time of the accident," he said, adding that "our objective today is to publish the first report by the end of June."

A series of automatic messages was sent by the plane's system just before it vanished, reporting lost cabin pressure and electrical failure. Arslanian said the messages were received in a time frame of three minutes. Investigators were working to interpret these messages, he added, saying that he did not want to go into details at such an early stage of the probe.

ABC News has also confirmed that two commercial planes flew virtually the same route as that taken by the Air France jet before and after the missing flight. According to a Lufthansa airlines statement, its flight in the area "operated normally without any irregularities reported by the crew."

French Transport Minister Jean-Louis Borloo said Tuesday he did not believe bad weather alone could have brought the plane down. He also brushed off the idea that terrorism or a hijacking could be involved.

Nance agreed that it would be almost unheard of for a plane to be downed by lightning alone but added, "You never say never."

Nance also said Tuesday it's unlikely that turbulence could 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.

AccuWeather's Ken Reeves said 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.

Roger Guiver, a former British Airways pilot, once lost weather radar on a flight from Capetown to London and opted to turn around when he encountered massive thunderstorms.

"Without the radar, as we got closer, we got a much better idea of the height of the clouds and it became obvious that it was not an option to fly over the top," Guiver said.

Searching for Clues About Missing Flight

Amaral said today the debris is spread out in two main areas, about 35 miles apart, located some 400 miles from the Brazilian islands of Fernando de Noronha.

Arslanian said one group of French investigators will search for debris and another three groups will study the plane's equipment and maintenance records. He emphasized that there were no suggestions of any problems with the plane before takeoff.

He also said he was "not optimistic" of recovering the aircraft's black boxes (cockpit voice and data recorders), which are believed to be buried under the sea.

If found, the plane's black boxes would provide many more clues about what happened. Experts said the black boxes emit pinging signals, although only for a finite period of time, in the water. With tracking beacons that activate when the boxes get wet, the black box radio signal works for about 30 days. But it won't be easy for search teams to pick up the signal and find a black box -- the size of the proverbial bread box -- in rocky terrain.

"It can be done, but I think we're gonna have to look for a little luck on this too," ABC News aviation consultant John Nance said today.

"They'll drop those microphones down quite a ways," Nance added.

The plane's cockpit voice recorder, made by Honeywell Aerospace, would have recorded the last two hours of conversation and would still be intact if found within the next 28 days -- even at a depth of 20,000 feet, according to Duncan Schofield, Honeywell's principle engineer of the black boxes. The flight data recorder may have recorded as many as 400 parameters.

But if stuck in a crevice on the mountainous ocean floor, he explained that the devices' pinging signals could be blocked. Honeywell's Bill Reavis said the boxes weigh about 13 pounds and don't float because "they are bolted to the tail." There is talk among lawmakers about experimenting with boxes that would break loose and float on impact.

Lt. Col. Jed Hudson, a commander at Tyndall Air Force Base in Florida, said that all planes also have emergency transmitters in their tails that are designed to send out distress signals 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, he said. The information can be stored and detected once satellites pass overhead -- unless it is too far underwater.

Mystery Over the Atlantic: The Passengers Onboard

According to the Brazilian air force, there's no indication that anyone survived.

The missing Airbus A330 had 216 passengers and 12 crew onboard when it took off Sunday night. All 12 crew members were French, according to the airline.

Passengers on the plane came from more than 30 countries, and included Americans Michael and Ann Harris, who had been living in Rio for more than a year. Tuesday afternoon, U.S. State department officials said a third American, a dual citizen traveling under a foreign passport, was also onboard.

In addition to the U.S. citizens, the passengers included 61 French citizens, 58 Brazilians, 26 Germans, nine Chinese and nine Italians. The group included seven children, a baby, 126 men and 82 women.

Michael Harris, a geologist working in Brazil for natural gas and oil producer Devon Energy, had 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."

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 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.

On Monday night a crew from TAM, Brazil's largest air carrier, said it saw orange spots on the ocean while flying over the same general area as the Air France Flight 447.

ABC News' Renata Araujo, Sonia Gallego, Joe Goldman, Christel Kucharz, Luis Martinez, Phoebe Natanson, Gabriel O'Rorke, Samira Parkinson-Smith, Kirit Radia and Christophe Schpoliansky, Reuters and The Associated Press contributed to this report.