Germanwings Flight 4U9525
Debris from Flight 4U9525 which clattered into the French Alps despite Captain Patrick Sondenheimer's desperate attempts to save his passengers Reuters

The captain of doomed Flight 4U9525, Patrick Sondenheimer, is being saluted as a hero as more details emerge of his efforts to wrest back control of the aircraft from co-pilot Andreas Lubitz.

The plane's cockpit voice recorder, which was rescued from the crash site, shows the father of two desperately trying save his passengers by smashing his way back into the locked cockpit with an axe.

Thirty minutes into the flight, the experienced 34-year-old captain had left his 27-year-old co-pilot, Andreas Lubitz, in control of the aircraft as he went to the toilet. The plane was cruising at an altitude of 38,000ft.

Upon his return, Sondenheimer found that the cockpit had been locked from the inside, and Lubitz had taken the plane down to 100ft by adjusting the autopilot.

Sondenheimer had been a pilot for more than a decade, racking up 6,000 hours of flight time on Airbus 320 planes.

"Between 09:30:52 and 09:30:55 you can see that the autopilot was manually changed from 38,000ft to 100ft and 9 seconds later the aircraft started to descend, probably with the 'open descent' autopilot setting," said Fredrik Lindahl, chief executive of Swedish tracking service FlightRadar24.

Sondenheimer knocked several times on the cabin door and asked to be allowed back into the cockpit.

After receiving no response from Lubitz, Sondenheimer tried to smash down the reinforced door with a fire safety axe, but to no avail.

The aircraft crashed into the French Alps at more than 400 mph.

A former colleague of Sondenheimer, named as Dieter by The Times, said: "I knew him well and he was one of the best.

"He was a very experienced pilot and his behaviour as a crew member was perfect. He was a very good man, a very nice man."