FERNANDO DE NORONHA, Brazil (CNN) — The first bodies to be recovered from the crash of Air France 447 returned to land Tuesday, as helicopters landed on the Brazilian archipelago of Fernando de Noronha, according to a CNN reporter on the scene.

Two Brazilian helicopters, each able to carry up to eight bodies, took off earlier to rendezvous with the Brazilian Navy ship carrying the recovered bodies.

Meanwhile, four more bodies were recovered Tuesday, according to the Brazilian air force, bringing the total to 28.

Air France 447 crashed in the Atlantic Ocean last week en route from Rio de Janeiro in Brazil to Paris, France, with 228 passengers and crew on board. It was the deadliest plane crash ever for Air France.

The cause of the crash is not yet known, but investigators are looking at the role of airspeed sensors known as pitot tubes, among other factors. Watch bodies being returned to land »

Air France has agreed to replace the sensors within days on all its Airbus A330 and A340 airplanes, a pilots’ union said Tuesday.

The airline said Saturday that it had begun replacing the sensors throughout its fleet in April. An Air France representative told CNN that the pilots’ union SNPL is meeting with company officials Tuesday afternoon and that the airline would not comment until after the meeting ended.

A smaller Air France pilots’ union, ALTER, has advised its pilots not to fly planes until their pitot tubes are replaced. Alter is the smallest of three pilots’ unions. It would not say what percentage of Air France pilots it represents.

The biggest union, SNPL, said Tuesday it accepted Air France’s assurances that no Airbus A330 or A340 will take off without at least two of the three pitot tubes replaced.

Union spokesman Eric Derivry added that there is no indication at this point that the pitot tubes were the cause of the accident.

Air France began to notice in May of 2009 year that pitot tubes sometimes briefly iced up at high altitude on A330s and A340s, the airline said in a statement Saturday. That caused “a loss of airspeed data,” according to the airline — that is, the pilot didn’t know how fast the plane was flying.

“Air France decided to replace all its probes” starting April 27, following laboratory tests earlier in the year, the airline said. The replacements are ongoing, and it is that program that the pilots say the airline has promised to complete within days.

France is sending a submarine to the suspected crash site to search for wreckage of the Airbus A330, including the flight data recorder and cockpit voice recorder — commonly known as black boxes. The United States is also sending equipment to help with the search, which aims to find the cause of the crash. Watch challenges faced by search crews »

The exact location of the crash has not been determined, since ocean currents likely have moved the bodies and debris. Map of Flight 447’s flight path »

The ocean depth where the debris and bodies have been found varies dramatically, but in general is about nearly 9,900 feet (3000 meters) deep, according to the University of New Hampshire/National Oceanic and Atmospheric Association Joint Hydrographic Center. The search area covers 77,220 square miles (200,000 square km), nearly the size of Romania, Brazilian officials said.

The ocean depth where the debris and bodies have been found is 6,000 to 8,000 meters (about 19,700 to 26,250 feet) deep, Brazilian military officials said. The search area covers 200,000 square km (77,220 square miles), nearly the size of Romania.

Brazilian officials emphasized Monday that finding bodies was their main priority. The French are in charge of finding the voice and data recorders.

Fourteen aircraft — 12 Brazilian and two French — were participating, along with five Brazilian ships and one French frigate. The U.S. Navy will contribute two high-tech acoustic devices to listen underwater for the emergency beacons that are attached to the voice and data recorders.

The “towed pinger locators” — which help search for emergency beacons on downed aircraft to a maximum depth of 20,000 feet — will be placed aboard two French tugs that are part of the search efforts, a U.S. defense official said.

Recovery of bodies and debris is significant not only for families, but also for crash investigators, said Mary Schiavo, a former inspector general for the U.S. Department of Transportation.

“Even if they don’t find anything else they can get some very important clues from the pieces that they do find and from the human remains,” she told CNN Saturday. Watch an explanation of what could have caused the crash »

She said investigators could determine whether there was an explosion by inspecting any residue on the bodies or other items. Or, if water is found in the lungs of victims, investigators would know the plane went down intact, she said.

Source: CNN http://edition.cnn.com/2009/WORLD/americas/06/09/brazil.plane.crash/index.html