The passengers who boarded Germanwings flight 4U 9525 at Barcelona's El Prat airport on Tuesday morning were the usual midweek mixture of tourists, business travellers and families, with a busy and, in some cases dramatic, morning already behind them by the time they settled into their seats. There were schoolchildren returning home from a Spanish exchange trip who had mislaid their passports and had to rush to catch the flight, parents negotiating about their babies, and frequent flyers.The ground crew responsible for the Airbus A320 were also having a busy morning. The aircraft had landed at 7.57am GMT with 122 passengers on board and was scheduled to take off for Düsseldorf at 8.35am. It had to be cleaned, refuelled, restocked and checked in less than 40 minutes.By 9.01am the Airbus was back in the air, on what should have been a 90-minute flight. All was normal for the next 40 minutes. The Airbus slowly climbed to its cruising altitude of 11600m, which it reached at 9.45am over southern France. But then something went catastrophically wrong.Less than a minute after reaching cruising altitude the aircraft went into a steep descent. The pilots did not ask air traffic control for permission to begin an unscheduled descent, and for the next eight minutes the aircraft plunged at a rate of 1200m a minute.Sébastien Giroud, who owns a sawmill, saw it. "The plane was flying very low, at maybe 1500m or 2000m," he said. "It seemed to be going down. I said to myself: 'It won't pass the mountains'."No Mayday signal was sent during that eight-minute fall.The aircraft remained intact, relaying its altitude, airspeed and heading and at 9.47am air traffic controllers implemented an aircraft distress alert, based on the plane's rapid loss of height.At 9.53am all contact was lost.The aircraft had flown into a mountain in the Alps, called Les Trois Eveches, between Digne-les-Bains and Barcelonnette, north-west of Monaco, and had "disintegrated", said one local official."It was a deafening noise. I thought it was an avalanche but it sounded slightly different," said Sandrine Boisse, president of the Pra Loup tourism office.Investigators have extracted cockpit voice recordings from one of the black boxes of the doomed airliner and expect to have a read-out of their content within days, an official said yesterday.The casing of a second black box has been found but not the box itself, French President Francois Hollande said as he arrived in the remote Alpine region with the leaders of Germany and Spain to pay tribute to the 150 victims...