For a second day, rescuers will fan out over harsh terrain in a remote corner of the French Alps looking for the remains of 150 people. So far, no one has been able to retrieve any bodies from Germanwings Flight 9525. And conditions for recovery efforts Wednesday are not ideal.
Although forecast snow now looks likely to fall higher in the mountains, low cloud and winds in the area where the plane went down a day earlier may impede the operation. Even without inclement weather, crews face an array of challenges in finding the remains of those on board: Near vertical mountain slopes. Tiny pieces of debris. Human remains strewn for hundreds of meters along a deep ravine.
It's also far from accessible. The plane crashed in an area known as the Massif des Trois-Eveches, near Digne-les-Bains, where mountain peaks soar almost as high as 3,000 meters (1.9 miles).
Helicopters took off Wednesday from Seyne-les-Alpes, the staging ground for search efforts. Officials say they need to fly helicopters to the crash site to allow teams to begin search and recovery efforts.
"Difficult conditions" hampered the progress of police overnight, French Interior Ministry spokesman Pierre-Henry Brandet told BFMTV. They must secure the site before investigators can get to work.
Merkel, Hollande and Rajoy arrived Wednesday afternoon at Seyne-les-Alpes to meet with rescue workers.
Perhaps the only task as challenging as recovering the bodies is figuring out why the plane went down with all 144 passengers and six crew members on board.
Germanwings employees held a moment of silence in Cologne, Germany, on Wednesday morning to mark the moment of the crash. A "small" number of flights were canceled due to reluctance among some crew members to fly, the airline said in a statement.
A moment's silence was also held in Barcelona, the Spanish city from which the plane took off, bound for Germany.
Strange factors in the crash
The crash of Germanwings Flight 9525 is bizarre for several reasons: There was no distress call. The aircraft crashed midflight, rather than at takeoff or landing like with most crashes. And the plane dropped from an altitude of 38,000 feet for eight minutes, the airline said.
Searchers have so far retrieved the cockpit voice recorder, one of the plane's two "black boxes," said Cazeneuve, the French interior minister. The device, which is designed to capture all sounds on a plane's flight deck, is damaged but not beyond use, he told French radio station RTL.
Aviation expert Geoffrey Thomas, editor-in-chief of AirlineRatings.com, told CNN that the damage "shouldn't be too much of a problem. Normally if they are damaged, we still get a lot of very valuable data from them, and in most cases, the data is still intact."
The cockpit voice recorder is particularly important, he said, "because we need to know what was going on (in) the cockpit and the challenges facing the pilots. ... This will tell us a lot about what went wrong."
The flight data recorder, which stores a vast array of information about the aircraft, is still missing. The two devices are expected to be crucial in unraveling what led to the crash. Investigators typically spend months analyzing the recorders' data.
Speaking after a Cabinet meeting Wednesday, Cazeneuve told BFMTV: "We cannot completely rule out terrorism, but it is not considered the most likely explanation at the moment. We need to let the investigation do its work."
The final moments of flight
One piece of information is already clear: There was no distress call from the cockpit, the French Civil Aviation Authority said. Why would a pilot not alert someone that there is an emergency? It might sound counterintuitive, but calling for help is not the first thing on a pilot's checklist when things go wrong.
Aviation analyst David Soucie said the first concern is to fly the plane, and secondly, to find the safest option for a crash landing, if it comes to that.
The Germanwings pilot "was definitely aviating and navigating from what we can tell," Soucie said. The pilot was conceivably looking for a place to try to land, he said. Flight 9525 was headed from Barcelona, Spain, for Dusseldorf, Germany.
According to Germanwings, the plane reached its cruising altitude of 38,000 feet, and then dropped for eight minutes. The plane lost contact with French radar at a height of about 6,000 feet. Then it crashed.
Slightly different timelines have emerged for the aircraft's final minutes. According to Germanwings, the plane started to descend without authorization at 10:45 a.m. (5:45 a.m. ET) and lost contact with French radar at 10:53 a.m., at a height of about 6,000 feet.
A spokesman for the French national police force told CNN the plane started to descend without authorization at 10:31 a.m. and that four minutes later air traffic controllers sent out a warning. The plane was registered at 2,000 meters (6,560 feet) but then disappeared from radar, he said.
"We heard a strange noise, and at first we thought it was an avalanche," said Sandrine Boisse, president of the tourism office at the Pra Loup ski resort said. "Something was wrong. ... We didn't know what."
German Foreign Minister Frank-Walter Steinmeier called the scene "a picture of horror" after flying over the area Tuesday.
Victims from around the world
While many victims have not been publicly identified, the names and stories of some are starting to emerge. Germanwings CEO Thomas Winkelmann said it's believed 72 people, or nearly half those on the plane, are German citizens. Another 35 are Spanish nationals, he said. But Francisco Martinez, Spain's secretary of state for security, said 49 Spaniards were aboard the flight, citing information from their families.
Winkelmann acknowledged his list, which includes only 125 victims out of the 150 presumed dead, is not complete.
The victims he listed included two nationals each from the United States, Australia, Argentina, Iran and Venezuela. There was one person on board from the United Kingdom, the Netherlands, Colombia, Mexico, Denmark, Japan, Belgium and Israel, he said. The UK Foreign Office earlier said three UK nationals had been on the plane.
Winkelmann said Germanwings had not yet managed to reach the families of 27 of the victims. The airline's priority is looking after the relatives of those killed and its own staff, he said.
"We are a small family. Everybody knows each other within Germanwings," Winkelmann said, adding, "The shock is immense."
Winkelmann said two special flights would take the relatives of those lost with the plane to southern France on Thursday, one from Dusseldorf and one from Barcelona, so they can be near the search scene.
Among the German citizens: 16 students and two teachers from a German high school called Joseph-Koenig Gymnasium, according to Florian Adamik, a municipal official in Haltern, the town where the school is located.
Haltern's mayor, Bodo Klimpel, said the students were headed home from a foreign exchange program.
The head teacher at a German school that lost 16 students and two teachers, Ulrich Wessel, told a news conference the crash had left him "almost speechless." Authorities are providing counselors and psychologists to help those at the school come to terms with the disaster.
Philippa, a friend of the German students, told CNN, "I knew all of them, they were all in my grade and there was a twosome I was very close to. We already planned things for the future -- what they were going to do when they returned from their trip so it's very hard to believe that we cannot do that."
A Mass was held Wednesday morning in Llinars del Valles, the Spanish town where the exchange students stayed, to mark the loss.
The Gran Teatre del Liceu in Barcelona posted a statement on its Facebook page saying two German opera singers who performed there this month in a production of "Siegfried," Oleg Bryjak and Maria Radner, had died in the crash.
Radner was returning to Germany with her husband and child, a spokesman for the production company said. Bryjak, a bass baritone, had performed in the Deutsche Oper am Rhein ensemble since 1996, the Dusseldorf opera house said on Twitter.
The theater will observe two minutes of silence for the victims Wednesday. An Australian mother and son, Carol and Greig Friday, who were holidaying together were among those killed, the Australian government said. A statement from family members said they were "in deep disbelief and crippled with sadness" at their loss.