A plane carrying 228 people falls out of the sky in the middle of the night hundreds of miles out to sea.
In this relatively early phase of the investigation into what happened on Air France Flight 447, here's a look at where things stand.
Where the Search Stands
Hunting for black boxes: T minus 18 days. The pinging sounds coming from the black boxes are estimated to last 30 days from the time of the crash, so the clock is ticking.
A French nuclear sub, the Emeraude, equipped with high-tech sonar equipment, is at the crash site listening for the acoustics coming from the flight data recorder and the cockpit voice recorder.
Scheduled to arrive Friday is a French research vessel called the Pourquoi Pas, the only vessel in the French arsenal that carries underwater robots to retrieve the black boxes if their signals are detected.
A U.S. Navy underwater listening device that can pick up the pinging sound from the black boxes at depths of 20,000 feet is also expected in the water Sunday.
Debris and remains: Crash remnants already pulled out of the Atlantic have been flown to the island of Fernando de Noronha, the closest land to the crash site, some 400 miles off Brazil's coast.
The bodies recovered will be analyzed on the island, then transported to the mainland town of Recife this weekend for further identification and forensic exams.
Number of bodies recovered: 41
Major debris recovered: A large chunk of the stabilizer from the plane's tail, wiring, an airline seat, a boarding pass from the flight.
How long the search will last: At least until June 19, according to the Brazilian Air Force.
Ocean currents and wind now play a part in recovery efforts because the crash happened more than a week ago. The Brazilian Air Force is calculating that ocean currents are carrying bodies north. The U.S. Coast Guard is helping map the debris field and tracing backwards to help locate the crash location.
Assessing the plane's automated messages: Out of the water, investigators are gleaning clues from the 24 automated messages sent from the plane to Air France over a period of four minutes before it crashed.
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
The Status of Possible Causes and Problems
"There is never, ever, just once cause to an airline accident," said ABC News aviation consultant John Nance. "Never has been, never will be."
Speed speculation: On Thursday, Agence France-Presse 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. On Thursday, 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 plane speed sensors on a number of Airbus jets.
Airbus recommended replacing the speed sensor 17 months ago after reports that they 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 on 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:
Lawmakers Examine Airline Safety (June 10, 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)