During the flight the Airbus was in contact with air control at Marseilles. The message was “mayday, mayday,mayday” and the pilot requested an emergency descent meaning ATC had to clear all air space below the route of the aircraft. Apparently, an emergency descent generally happens at a rate of 5,000 feet a minute, but the Germanwings flight was descending at 3,375 feet a minutes.
Gerard Feltzer, an aviation expert told BFM TV that the plane was already extremely low when it issued its distress signal and he imagined the pilots had tried to deal with the emergency before issuing their message, at which point it appeared they had already lost control of the aircraft.