RECIFE, Brazil – The recovery of Air France Flight 447's tail section could provide key clues as to why the airliner with 228 people on board went down in the Atlantic and where best to search for the black boxes, experts said.
The tail section includes the vertical stabilizer — which keeps the plane's nose from swinging back and forth — and the rudder, which generates and controls the side-to-side motion of an aircraft.
The data and voice recorders are located in the fuselage near the tail.
In a video posted Monday on a Web site, Brazil's air force revealed that search crews had recovered the vertical stabilizer from the tail section of the plane. Brazilian military officials have refused to detail the large pieces of the plane they have found.
Eight more bodies also were found, bringing the total recovered to 24, Air Force Col. Henry Munhoz said. The plane disappeared during a flight from Rio de Janeiro to Paris on the night of May 31 with 228 people on board.
The Air Force video, titled "Vertical Stabilizer Found," shows the piece being located and tethered to a ship. The part had Air France's blue-and-red stripes, was still its original triangular shape and was not visibly burned.
William Waldock, who teaches air crash investigation at Embry-Riddle Aeronautical University in Prescott, Arizona, examined the photos and video of the stabilizer and rudder and said the damage he saw looks like a lateral fracture.
"That would reinforce the idea that the plane broke up in flight," he said. "If it hits intact, everything shatters in tiny pieces."
That there were no signs of burn marks on the stabilizer is not necessarily significant, according to Waldock, who said that any explosion or fire in the fuselage would likely not make its way back to the tail section. Examining the fracture surfaces is important, since they will indicate from what direction the force came that snapped the piece, he said.
Peter Goelz, a former managing director of the National Transportation Safety Board, said recovered passenger bodies also will play a role. If investigators can determine the identity of a body and know where that person was sitting in the plane, the types of injuries sustained could offer clues into the crash, he said.
The investigation into TWA Flight 800, which crashed off the coast of Long Island, New York, in 1996, found that victims sitting in front of row 30 sustained flash burns. Goelz said that helped investigators confirm that the nose broke off and fire blew back from the fuel tank onto those passengers.
The discoveries of debris and the bodies also are helping searchers narrow their hunt for the cockpit voice and data recorders, commonly known as the "black boxes," perhaps investigators' best hope of learning what happened to the flight.
Waldock said the black boxes won't necessarily be located near where the debris was recovered, "but finding the tail narrows down the area even further."
The wreckage and the bodies were found roughly 400 miles (640 kilometers) northeast of the Fernando de Noronha islands off Brazil's northern coast, and about 45 miles (70 kilometers) from where the jet was last heard from on May 31.
Searchers must move quickly to find the recorders because acoustic beacons, or "pingers" on the boxes begin to fade 30 days after crashes.
Some high-tech help is on the way for investigators: two U.S. Navy devices capable of picking up the pingers to a depth of 20,000 feet (6,100 meters).
The listening devices are 5 feet (1.5 meters) long and weigh 70 pounds (32 kilos). One will be towed by a Brazilian ship, the other by a French vessel, slowly trawling in a grid pattern across the search area. The devices will be dropped into the ocean near the debris field by Thursday, Berges said.
Cables attached to the devices lead to on-board computers, enabling a 10-person team that accompanies each device to listen for pings and to visually see them on a screen, like a radar spotting objects in the air.
The French nuclear attack submarine Emeraude, arriving later this week, also will try to find the acoustic pings, military spokesman Christophe Prazuck said.
If the pings are located, French deep-water unmanned subs aboard the oceanographic survey ship Pourquoi Pas will attempt to retrieve the boxes from the ocean floor.
Crash theories being considered by investigators include the possibility that external speed monitors — called Pitot tubes — iced over and gave dangerously false readings to cockpit computers in a thunderstorm.
Goelz said the faulty airspeed readings and the fact the vertical stabilizer was sheared from the jet could be related.
The Airbus A330-200 has a "rudder limiter" which constricts how much the rudder — which is attached to the vertical stabilizer — can move at high speeds. If it were to move too far while traveling fast, it could shear off and take the vertical stabilizer with it.
"If you had a wrong speed being fed to the computer by the Pitot tube, it might allow the rudder to over travel," Goelz said. "The limiter limits the travel of the rudder at high speeds and prevents it from being torn off."
Asked if the rudder or stabilizer being sheared off could have brought the jet down, Goelz said: "Absolutely. You need a rudder. And you need the (rudder) limiter on there to make sure the rudder doesn't get torn off or cause havoc with the plane's aerodynamics."
The L-shaped metal Pitot tubes jut from the wing or fuselage of a plane, and are heated to prevent icing. The pressure of air entering the tubes lets sensors measure the speed and angle of flight. An iced-over, blocked or malfunctioning Pitot tube could cause an airspeed sensor to fail, and lead the computer controlling the plane to accelerate or decelerate in a potentially dangerous fashion.
A memo sent to Air France pilots by the Alter union Monday and obtained by The Associated Press urges them to refuse to fly unless at least two of the three Pitot sensors on each planes have been replaced.
An official with the Alter union, speaking on condition of anonymity because the memo was not publicly released, said there is a "strong presumption" among its pilot members that a Pitot problem precipitated the crash. The memo says the airline should have grounded all A330 and A340 jets pending the replacement, and warns of a "real risk of loss of control" due to Pitot problems.
Air France said it began replacing the Pitot tubes on the Airbus A330 model on April 27 after an improved version became available, and will finish the work in the "coming weeks." The monitors had not yet been replaced on the plane that crashed.
The leader of another pilots' union, however, said Monday that Pitot troubles probably didn't cause the Flight 447 disaster.
In addition to the vertical stabilizer and numerous bodies, searchers have spotted two airplane seats and debris with Air France's logo, and recovered dozens of structural components from the plane.
Brazil says the search area lies southeast of the jet's last transmission — automatic messages signaling catastrophic electrical failure and loss of cabin pressure. The messages mean Flight 447 likely broke apart in turbulent weather. The location of the wreckage could mean the pilot was trying to turn around in mid-flight.
France's defense minister and the Pentagon have said there were no signs that terrorism was involved in the crash.