The black boxes, the size of a proverbial bread box, can survive in up to 20,000 feet of water, and they emit a pinging sound. But water temperatures can affect the distance that sound travels, and the mountainous ocean floor can block the signal, which is only guaranteed to last about 26 more days.
The information the black boxes hold is critical: The cockpit voice recorder would have the last two hours of conversation recorded; the flight data recorder could hold information about as many as 400 systems on the plane to help investigators piece together the puzzle.
"We have to find that," Nance said. "This is a whole new class of airplane, not just the Airbus, but Boeings like it. We have to know what happened."
"It's down there," Nance said. "It'll be mangled, but it's down there."
"If they can't get that black box, they've got quite a detective story to sort out to try to determine the cause," Ballard said.
U.S. accident investigators have been asked to assist in the recovery effort. Several other teams of people on planes and ships are also making their way to the remote crash site some 400 miles from Brazil's Fernando de Noronha islands, carrying equipment to recover debris. A French search and exploration ship, due on site Friday, is equipped with robots that can plunge about 20,000 feet underwater to help recover wreckage.
"Heavy objects will go to the bottom very, very rapidly," Ballard said. "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."
But recovering debris in this part of the ocean may not be easy.
"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.
"There is never, ever just one cause to an airline accident," Nance said. "Never has been, never will be."
Developments this week have confirmed the complexity of the puzzle as searchers pinpoint debris and assess the weather.
"I can't remember an accident in quite some time, if ever, that has raised the level of concern in the pilot community as much as this one has," Nance said.
"Those of us who are pilots are really apprehensive about what happened here because when you're out over the water at altitude, this sort of thing is never supposed to happen," he added.
Confirmed by the pilot's message, the plane is thought to have encountered severe 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.
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.
Still, Ken Reeves, director of forecasting operations at Accuweather.com, said towering thunderstorms, fairly common over that area of the Atlantic, could have been a challenge.