Dusseldorf, Germany - Emergency responders managed to retrieve the black box from Flight 4U 9525 before nightfall as snow hindered recovery operations at the crash site of a German airliner that went down in the French Alps on Tuesday, leaving all 150 passengers and crew presumed dead.

Investigators said they were operating on the initial assumption that a technical or other failure had caused the crash, whose victims included two infants, an opera singer and vacationers as well as a group of German 10th graders returning from a school trip to Spain.

The Airbus 320 operated by Germanwings, the budget arm of the German carrier Lufthansa, had left Barcelona en route to Dusseldorf nearly 30 minutes late for reasons that remained unexplained. It traveled on a normal flight path before suddenly shifting into a steep descent only moments after reaching its cruising altitude of 38,000 feet.

Within eight minutes, the plane had lurched down to 6,000 feet before falling off French radar screens at 10:53 a.m. local time. The pilots, French officials said, had not signaled air traffic control immediately before or during their sudden descent. The plane then crashed into rugged mountain terrain near the French ski resort of Prads-Haute-Bléone, where rescue workers and officials described a tableau of pulverized devastation.

"The site is a scene of horror,"said Frank-Walter Steinmeier, Germany's foreign minister, after a flight over of the crash zone.

The disaster put a new focus on the A320, a workhorse of the skies that has now been at the center of a dozen fatal accidents since 1988. On Tuesday, European leaders launched a major international investigation to establish the cause of a crash involving an airline group - Lufthansa - long known for its strong safety and maintenance standards but which in recent months has been dogged by bouts of labor unrest.

Crews using helicopters sought to access the hard-to-reach site where aerial photos showed debris scattered across a 5-acre expanse of frigid outcroppings. At least 10 coroners from the city of Marseilles were en route to the town of Seynes-les-Alpes to receive the bodies of victims. A stream of high-level ministers and leaders from across Europe were heading to cities near the crash zone, and an official from Lufthansa said the company was weighing an offer to transport family members to the area.

European leaders, meanwhile, tried to piece together the cause of Western Europe's worst commercial air disaster in recent years.

In one hopeful sign, one of two black boxes was recovered and was being shipped to Paris for analysis. It remained unclear whether the device found was the voice recorder capturing the last minutes of conversation in the cockpit or the data recorder with information from plane sensors.

"It's a tragedy on our soil," said French President François Hollande, who was hosting Spain's King Felipe VI and Queen Letizia on a state visit at the time of the crash. The Spanish monarchs cut short their visit to return to Madrid amid what was shaping up to be a pan-European disaster response.

In Washington, a statement from a spokeswoman for the U.S. National Security Council, Bernadette Meehan, said there was "no indication of a nexus to terrorism at this time." Two European intelligence officials, who spoke on condition of anonymity because of the ongoing probe, also said there were no immediate indications of terrorism.

The A320 enjoys a track record as one of the safest jets in the skies. For every million takeoffs, the A320 fleet has about 0.14 fatal accidents, according to a Boeing study that analyzed five decades of air disasters. That puts it on par with the Boeing 777 as one of the most reliable commercial planes.

Yet the crash on Tuesday follows a number of high-profile A320 crashes including the loss in December of an AirAsia jet in the Java Sea, killing 162 passengers and crew during severe thunderstorms. Weather, however, was reported to have been clear and calm in the vicinity of the Germanwings flight on Tuesday.

Responding to German media speculation that a computer glitch could have forced the plane into a steep dive, Germanwings officials said they believed that had not caused the crash and that the A320's computer systems were fully updated.

Asked if the airline would ground its A320s, Germanwings chief executive Thomas Winkelmann said the planes have a "fabulous service record."

He said the aircraft lost Tuesday flew its first flight in 1990 and was purchased by Lufthansa in 1991. It was transferred to its discount brand, Germanwings, last year, and has flown 583,000 hours across 46,700 flights.

That makes it one of the older A320s but still within the average age of planes in service. Its last routine maintenance check, the company said, had taken place on Monday in Dusseldorf, with the last fuller inspection of the aircraft in the summer of 2013.

The flight's captain, he said, had more than 10 years of experience with Lufthansa and Germanwings and had logged more than 6,000 flight hours.

The plane's descent was sudden but still took eight minutes. Some experts wondered why no distress signal was sent during that period. Others countered that no mayday would have been likely if the pilots were busy managing a catastrophic error. More surprising for some was that the plane ran into trouble mid-flight.

"The plane was cruising at 38,000 feet - planes don't crash in cruise," said Anthony Davis, a London-based aviation specialist. "They crash in take-off or landing or they have engine failure, but it's very unusual anything should happen at that altitude."

Following word of Tuesday's crash, reception and information centers for family of victims were quickly set up in Barcelona and Dusseldorf, where confused passengers lingered around Germanwings counters well into the evening. The company operates largely short-haul flights within Europe for cost-conscious travelers and said at least 30 flights were canceled after a smattering of emotionally rattled Germanwings crew declined to fly following the crash.

Authorities said 40 to 50 distraught family members had arrived at the airport in Dusseldorf and were being greeted by company officials and psychologists in a private location off limits to the press.

A full passenger list had yet to be released, but Winkelmann said 67 of the passengers appeared to be German nationals. The Deutsche Oper am Rhein said one of its baritones, Oleg Bryjak, had been on board the flight. Germany, though, was gripped with the story of a group of 16 10th grade students and two teachers from Joseph König High School in Haltern, Germany, who, according to Bodo Klimpel, mayor of the town in North Rhine-Westphalia, were also on the plane.

The students had been on a one-week language exchange trip in Spain. A news broadcast by the German public TV network ARD showed groups of students standing in the school yard, looking distraught and lighting candles.

"These events are so terrible that we haven't processed them yet," the school's principal, Ulrich Wessel, told journalists in Haltern, urging them to respect the students' privacy.

European officials also said at least 45 passengers were Spanish nationals, one was Belgian and an unknown number were Turkish and British.

"We will work together with authorities and give our utmost to investigate and resolve the cause of the accident as quickly as possible," Winkelmann said.