If there is ever to be an answer to what caused Air France Flight 447 to fall from the sky, the best clues probably lie on the floor of the Atlantic Ocean amid rugged volcanic ridges and steep trenches, some plunging deeper than the Grand Canyon.
Search planes scouring the area Tuesday spotted a seat, an orange buoy, a tank and a fuel slick about 400 miles off the Brazilian coast. Brazilian authorities identified them as pieces from the Airbus A330 that disappeared late Sunday, and French officials reiterated that there was virtually no chance that any of the 228 people aboard survived.
Most of the wreckage is probably resting now 9,000 feet to 14,000 feet below the surface, where it is pitch black, the water temperature is 40 degrees and the pressure as high as 7,000 pounds per square inch, scientists said.
Investigators will have to send robotic submarines into this hostile environment to look for crucial pieces of evidence in the disappearance of the Paris-bound flight.
A battery-operated sonar "pinger," 4 inches long and about an inch in diameter, should already have started sending out acoustic signals from the ocean bottom about once every second. The pinger is attached to the flight data recorder, which is embedded in the rear section of the jetliner's fuselage. Another pinger is attached to the cockpit voice recorder.
Even with the help of those homing signals, the task of finding the debris amid the rugged seascape will not be easy, experts said. And if searchers find them, they will face challenges reaching the wreckage and determining what happened.
"You want to treat it like a crime scene, taking detailed photographs," said Dave Gallo, director of special operations at Woods Hole Oceanographic Institution in Massachusetts. "In the past, the urge was to remove evidence as quickly as possible, but before you disturb anything you want a detailed survey."
The floating debris was spotted north of the archipelago of Fernando de Noronha off the Brazilian coast, suggesting that the plane disappeared not long after it last radioed its position.
But wind and ocean currents may have pushed the floating debris miles from the impact point in the intervening day, and it will be difficult for investigators to pinpoint the location of the most important pieces of evidence, the two so-called black boxes that record flight data and the voices of the pilots.
