So Sad- Germanwing co-pilot deliberately crashed the plane

The co-pilot of the doomed Germanwings Airbus A320 locked his captain out of the cockpit before deliberately crashing into a mountain to 'destroy the plane', it was sensationally revealed today.

French prosecutor Brice Robin gave further chilling details of the final ten minutes in the cockpit before the Airbus A320 plunged into the French Alps killing 150 people.

Revealing data extracted from the black box voice recorder, he said the co-pilot - 28-year-old German Andreas Lubitz - locked his captain out after the senior officer left the cockpit.

At that point, Lubitz used the flight managing system to put the plane into a descent, something that can only be done manually - and deliberately.

He said: 'The intention was to destroy the plane. Death was instant. The plane hit the mountain at 700kmh (430mph).

'I don't think that the passengers realised what was happening until the last moments because on the recording you only hear the screams in the final seconds'. 

Earlier in the flight, Mr Brice said Lubitz's responses, initially courteous, became 'curt' when the captain began the mid-flight briefing on the planned landing of the plane.

The captain - named by local media as German father-of-two Patrick Sonderheimer - then left the cockpit but found himself locked out when he tried to re-enter.

Mr Robin said: 'We hear the pilot asking the co-pilot to take over and we hear the sound of a chair being pushed back and a door closing so we assume that the captain went to the toilet or something.

'So the co-pilot is on his own, and it is while he's on his own that the co-pilot is in charge of the plane and uses the flight management system to start the descent of the plane.

'At this altitude, this can only be done voluntarily. We hear several shouts from the captain asking to get in, speaking through the intercom system, but there's no answer from the cockpit.' 

Mr Robin said Lubitz 'voluntarily' refused to open the door and his breathing was normal throughout the final minutes of the flight.

He said: 'His breath was not of somebody who was struggling. He never said a single word. It was total silence in the cockpit for the ten past minutes. Nothing.'  

Air Traffic Control at Marseille asked for a distress signal, but there is still no response, said Mr Robin.

He added: 'So the plane becomes a priority for a forced landing.

'Control asks other planes to contact this Airbus and no answer is forthcoming.

'There are alarm systems which indicate to all those on board the proximity of the ground. Then we hear noises of someone trying to break into the door. 

'The door is reinforced according to international standards.'