The mystery of flight 9525: a locked door, a silent pilot and a secret history of illness
It was a promise they were prevented from keeping. Just under 40 minutes into their journey, the plane's 27-year-old co-pilot, Andreas Lubitz, turned the Airbus A320 into a missile, guiding it into the southern Alps after locking its captain, Patrick Sonderheimer, out of the cockpit.
In the doomed flight's final minutes, Sonderheimer attempted to force his way through the security door that separates the passengers from the pilots. At one stage he reportedly tried to use an axe. Recordings obtained by crash investigators capture him attempting to remonstrate with Lubitz - whose breathing, according to the microphones in the cockpit, remained sure and steady as the plane made its rapid descent. It was only in the final seconds that there was the sound of screams. Experts said death would have been instant.
For the families of the 150 people who perished, this is the only thin comfort to be grasped in a grotesque tragedy, the first crash of a large passenger jet in France since the Concorde disaster outside Paris nearly 15 years ago.
Within minutes of the plane going down, a frightened world was scrambling for answers. The A320 is the workhorse of the aviation industry and is considered one of its safest planes. Every two seconds of every day, one takes off or lands somewhere.
In Washington, the White House was quick to suggest that the crash did not appear to have been caused by a terrorist attack, while Lufthansa said it was working on the assumption that it had been an accident, adding that any other theory would be speculation.
One popular theory was that the cockpit windscreen had shattered. Another suggested mechanical failure. But there were many unanswered questions. Why had the pilots not issued a mayday? Why, if a mechanical failure had made it impossible to stop the plane from dropping, had they failed to alter course and swerve away from the mountains? And why had they failed to respond to repeated and increasingly frantic calls from air traffic controllers and other aircraft?
It was a mystery. As one former pilot told French television: "The pilots must have been unconscious, or dead, or forced by someone to fly the plane straight into the mountain."
Speculation had reached fever pitch by 5pm on the afternoon of the crash when it was announced that one of the black boxes - the cockpit voice recorder - had been found and would be sent to the French air accident investigation bureau just outside Paris, an operation that inexplicably took until 9.45 the following morning.
The suspense was intense. The black box had been damaged in the 435mph impact and there were doubts it would yield any information. The announcement by Rémi Jouty, the bureau director, that "sounds, voices, alarms" had been extracted from it, sparked enormous relief. Jouty said he was optimistic that accident investigators would solve the mystery but refused to say more and became tetchy when asked to elaborate. It was, in his precisely translated words, "much too soon to draw the slightest conclusion about what happened".
But even as he was speaking, investigators were becoming aware of what had happened to flight 9525.
As the New York Times revealed early on Thursday, French time, the voice recorder confirmed that Lubitz had locked the captain out of the flight deck and set the plane on its descent. The bureau battened down the hatches and refused to comment.
There were claims that the investigators, who come under the authority of the transport ministry, had been leant on to delay revealing its findings, to allow someone high-profile to break the "exclusive". The French pilots' union was outraged at the leak to the paper and announced that it was taking legal action to find out who had breached investigation secrecy rules.
Brice Robin, the French public prosecutor appointed to head the crash investigation, had not been immediately informed either, and was also angry. Robin began his press conference on Thursday saying that he had received the information he was about to give "a bit late for my liking", but his irritation was quickly overshadowed by the extraordinary information he then released.
As Robin outlined slowly and clearly the grim and almost unbelievable events that brought the plane down, a sense of shock and incredulity spread around Europe and beyond. Half of the 150 victims of Tuesday's disaster were German, with Spain accounting for at least 50, but the dead came from more than a dozen countries.
Politicians found themselves struggling for words. France's prime minister, Manuel Valls, said that all the signs were "pointing towards an act that we can't describe: criminal, crazy, suicidal". German chancellor Angela Merkel said the conclusions brought the tragedy to a "new, simply incomprehensible, dimension".
Comparisons were quickly made with the doomed flight MH370 that plunged into the Indian Ocean last year and has never been found. Many believe that plane was deliberately brought down, a scenario that is rare but not unprecedented.
In November 2013, a flight between Mozambique and Angola crashed in Namibia, killing 33 people. Initial investigations suggested the accident was deliberately caused by the captain shortly after his co-pilot had left the flight deck. In October 1999, an EgyptAir Boeing 767 went into a rapid descent 30 minutes after taking off from New York, killing 217 people. An investigation suggested that the crash was caused deliberately by the relief first officer, although the evidence was not conclusive. And in December 1997, more than 100 people were killed when a Boeing 737 flying from Indonesia to Singapore crashed; the pilot, who was said to be suffering from "multiple work-related difficulties", was suspected of switching off the flight recorders and intentionally putting the plane into a dive.
But many who knew Lubitz were quick to defend him from being placed in the same category, saying that they did not believe he would have intentionally downed a plane in a deliberate act of mass murder.
Neighbours in his small home town of Montabaur in the Rhineland, where he lived some of the time with his parents, described him as a keen runner in excellent physical health. Several said they had seen him in the weeks before the crash and remarked that he seemed untroubled.
But this picture was contradicted dramatically by his ex-girlfriend. In an interview with the bestselling German tabloid Bild, the 26-year-old flight attendant, known only as Maria W, said that they had separated "because it became increasingly clear that he had a problem". She said that he was plagued by nightmares and would wake up and scream "we're going down".
Last year he told her: "One day I'm going to do something that will change the whole system, and everyone will know my name and remember."
Bild also reported that Lubitz had sought psychiatric help for "a bout of serious depression" in 2009 and was still receiving assistance.
A search of his parents' home, and an apartment he kept in Düsseldorf, unearthed what prosecutors describe as "medical documents that suggest an existing illness and appropriate medical treatment". The documents included "torn-up and current sick leave notes, among them one covering the day of the crash".
Carsten Spohr, chief executive officer of Lufthansa, Germanwings' parent company, said that Lubitz had suspended his pilot training "for a certain period", before restarting and qualifying for the Airbus A320 in 2013.
On Saturday the New York Times reported that Lubitz had sought treatment for vision problems "that may have jeopardised his ability to continue working as a pilot", according to two officials with knowledge of the investigation.
Lubitz's ex-girlfriend suggested that if he did deliberately crash the plane, it was "because he understood that ... his health problems, his big dream of a job at Lufthansa, as captain and as a long-haul pilot, was practically impossible."
Mental health charities have urged people to avoid linking depression with murderous acts. But it is clear that understanding Lubitz's psychology will form an integral part of an investigation that will shine a spotlight on the pressures facing today's pilots.
"This tragedy has opened a window into the issues of pilot pressures and mental health," tweeted Brendan O'Neal, chair of pilots' union Balpa. "No kneejerk but the issues are real."
A debate now rages about the extent to which companies and regulators can monitor a person's mental health, especially if they perform a job that carries responsibility for the lives of others. The UN world aviation body has stressed that all pilots must have regular mental and physical checkups. But psychological assessments can be fallible. "If someone dissimulates - that is, they don't want other people to notice - it's very, very difficult," Reiner Kemmler, a psychologist who specialises in training pilots, told Deutschlandfunk public radio.
The task of sifting through Lubitz's back story, trying to discern the causes of his actions, is almost as complex as the forensic combing of the crash site. French police said that they have so far recovered between 400 and 600 pieces of human remains.
Colonel Patrick Touron of the Gendarmerie Nationale said DNA samples had been taken from objects provided by victims' families, such as combs or toothbrushes, that could help identify their loved ones. "We haven't found a single body intact," said Touron, who explained that the rough terrain meant that recovery workers must be backed up by mountain rescuers. "We have particularly difficult conditions, and each person needs to be roped up," he said.
There is speculation that Lubitz picked the crash site intentionally. He is known to have visited the region regularly as a member of a gliding club.
Already, the tragedy has prompted a shake-up of airline safety rules. The European Aviation Safety Agency has recommended that at least two people are present in the cockpit at all times, something already standard in the US.
German authorities have agreed to the rule for Lufthansa, its subsidiary Germanwings, and other companies. Austria and Portugal also announced that they would be requiring the adoption of the "rule of two", which has been backed by Air France, KLM, Britain's easyJet, Brussels Airlines and Norwegian Air Shuttle, among other airlines. Ireland's Ryanair, Finland's Finnair and Spanish carrier Iberia already adhere to the rule, for full story go to the Guardian.com .