Air France: Where Things Stand as Black Box Signals Fade

It's been nearly four weeks since Air France flight 447 crashed into the Atlantic Ocean enroute to Paris from Rio de Janeiro. Search teams are now racing against the clock to find the most vital clues to the crash -- the plane's black boxes -- before their signals fade.

At the same time, the National Transportation Safety Board this week is investigating two other incidents involving Airbus A330 planes like the one that crashed. The safety board wants to learn more about reported problems with airspeed and altitude information. It's known there were faulty airspeed readings on the Air France flight before the accident, and that's been a focus of the investigation.

Here's the latest on where things stand:

Evidence Recovered:
50 bodies. The body of the pilot and that of a flight attendant are among those that were identified this week.

Hundreds of pieces of debris. A large chunk of the stabilizer from the plane's tail, wiring, an airline seat, a boarding pass, personal belongings.

Evidence Not Recovered:
The two most important clues to the mystery -- the flight data recorder and cockpit recorder -- known as the plane's black boxes. Their batteries are required to last 30 days from the time of the crash. It's already been 26.

The Hunt for the Black Boxes:
Earlier this week there were reports that sounds heard underwater were coming from the black boxes. But France's investigation bureau issued a statement Tuesday saying "no signals transmitted by the flight recorders' locator beacons have been validated up to now."

The company that makes the black boxes say they could emit pinging sounds a little bit longer than 30 days, but will eventually fade out. France's investigation bureau is hopeful they black boxes will continue to transmit signals beyond that time frame and will continue the underwater search "as long as there will be a reasonable effort."

The world's best teams and equipment are in the remote Atlantic Ocean trying to detect the signals. The French nuclear sub Emeraude, equipped with high-tech sonar equipment, is listening for the acoustics, as is a U.S. Navy underwater listening device that can pick up the pinging sound from the black boxes at depths of 20,000 feet. A French research vessel, the Pourquoi Pas, is on hand with underwater robots to retrieve the black boxes if the signals are heard.

Latest Analysis of the Evidence:
This week investigators said they'd identified about more than a dozen of the 50 bodies recovered.

Autopsies on the bodies being examined reveal multiple fractures of passengers' legs, hips and arms. The evidence indicates the plane may have come part in the air as opposed to breaking apart when it hit the water.

Large pieces of the plane collected also indicate a midair breakup.

Experts also say bodies are not burned, which suggests there was not an explosion. But they also say that while the bodies may provide clues, it's unlikely they will indicate the probable cause of the crash on their own.

Crash remnants pulled out of the Atlantic were flown to the island of Fernando de Noronha, the closest land to the crash site, some 400 miles off Brazil's coast. From there they are being transported to the mainland town of Recife for further analysis. The tail stabilizer of the plane, a huge piece of evidence, arrived in Recife June 14.

A French technician in Recife is analyzing the evidence and will determine whether debris will be taken to France or evaluated in Brazil.

How Long the Search Will Last:
According to Agence France Presse, France's investigation bureau will keep searching for the black boxes after June 30 as long as it will represent a "reasonable effort," the bureau indicated Wednesday.

The bureau also said it would release its first factual report on what happened on July 2.

The water is warm, about 82 degrees Fahrenheit, which means bodies are more likely to float.

See ABC News photo gallery of the search effort here.

Watch ABC News Video on the Crash:
Air France Crash Questions Sensor Safety (June 9, 2009)
Search Intensifies for Black Boxes (June 8, 2009)
Plane Disappears Off Radar (June 1, 2009)

Read ABC News Stories on the Crash:
French Sub Joins Black Box Search (June 10, 2009)
Carriers Rush to Replace Speed Sensors (June 9, 2009)
Jet's Tail Could Lead to Answers (June 8, 2009)
Air France Official: 'We Can Fear the Worst' (June 1, 2009)

Air France 447: A Guide to the Tragic Crash

Airline Safety Measures Taken Since the Crash:
Air France has replaced speed sensors on its planes. Airlines, including Delta, US Airways and United are also rushing to finish replacing their sensors, a noncritical change recommended by Airbus 17 months ago. Faulty speed readings can cause the jet to fly dangerously slow or fast.

Status of Possible Causes and Problems
Speed speculation: Agence France-Presse has reported that there is "still no established link" between the plane's speed sensors, called pitot tubes, and the crash, according to a spokeswoman for the Bureau Enquetes Analyses, France's equivalent of the National Transportation Safety Board.

Accident investigators have said speed sensors malfunctioned on the flight, and the problem could have caused the plane to fly dangerously slow or fast. Last week, Pierre-Henri Gourgeon, Air France-KLM managing director, said, "We cannot, however, assume any link between the sensors and the causes of the accident." Meantime, airlines worldwide, including Delta, US Airways and United, are scrambling to replace speed sensors on a number of Airbus jets.

Airbus recommended replacing the speed sensor 17 months ago after reports that they'd malfunctioned or iced over, but it wasn't an urgent problem. On Monday, June 8, Airbus sent a note to its customers specifying that the Airbus A330 and A340 were "safe," even if still equipped with the older speed sensors. The sensors had not yet been changed on Air France Flight 447.

The terrorism hypothesis: Reports surfaced June 10 that two passengers on the plane had the same names as radical Muslims on France's watch list. French interior ministry spokesman Gerard Gachet denied this lead to ABC News the same day. Federal police in Rio said June 5 that they had confirmed all passengers on the flight had been checked as part of the effort to rule out terrorism.

But it's too early to rule out terrorism entirely, officials have said. On June 5, French Defense Minister Herve Morin said there was "no element or lead that would allow to corroborate this, but the ongoing investigation never ruled out this because the main threat today against our democracies is terrorism."

A bomb threat on an Air France flight from South America to Paris fueled speculation about terrorism, but there is no evidence of a similar threat to the accident flight. The threatened May 27 flight from Buenos Aires to Paris was inspected before takeoff and was allowed to depart after investigators found nothing of concern.

Weather worries: Meteorologists say the plane's flight path would have taken the jet right through a series of towering thunderstorms. High thunderstorms that develop quickly are common over this part of the ocean and would have been difficult to fly above. Aviation experts have said it would be exceedingly unusual for lightning alone, or severe turbulence alone, to bring the plane down, but have said it's possible weather may have played a part. The jet was equipped with sophisticated radar to help dodge troublesome storms.

Plane Crash Over the Atlantic: What We Know for Sure

The plane departed from Rio de Janeiro to Paris on May 31 carrying 228 people. Its last communication came nearly four hours into its journey.

The pilot sent an electronic text message to the airline saying the plane was flying through turbulent weather. That was in an area called the Intertropical Convergence Zone and it is known for thunderstorms and stormy weather.

A series of 24 automated messages over four minutes was sent from the plane shortly before it vanished, documenting a series of systems failures including lost cabin pressure and electrical failure. The messages also indicated variable speed readings, possibly indicating a problem with the instruments that measure the speed of the aircraft.

The captain of the flight had more than 11,000 hours of flight time, including 1,700 hours on this type of plane, according to Air France.

The Airbus jet was four years old.

More from ABC News on airline safety:
Plane Lands After Pilot Dies In-Flight (June 18, 2009) Death Knell for Geese Near N.Y. Airports (June 17, 2009)
FAA Holds Regional Airline Safety Summit (June 15, 2009)
Capt. Sully Sullenberger Recounts Landing on Hudson River (June 9, 2009)
Regional Airlines Under Scrutiny (May 14, 2009)
The Black Holes of Plane Crashes (June 4, 2009)
Fear of Flying Causes Families to Split Flights (June 4, 2009)

ABC News' Lisa Stark, Christophe Schpoliansky, Zoe Magee, Ammu Kannampilly, Renata Araujo and The Associated Press contributed to this report.