Reports have suggested the Germanwings co-pilot Andreas Lubitz had suffered from mental health issues and may have been receiving treatment for vision problems before he flew the plane into the mountain range.
Lubitz deliberately crashed an Airbus A320 into the French Alps last week, killing all 150 people on board.
The New York Times cited unnamed German sources as saying that Lubitz (27) may have been receiving treatment for an unspecified vision problem which could have affected his ability to carry on working as a pilot.
Authorities have already revealed that he hid from his employers a sick note declaring him unfit to work on the day of the disaster and German newspaper Bild has said he previously told an ex-girlfriend: “One day I will do something that will change the whole system, and then all will know my name and remember it.”
According to Bild, Lubitz was going through a "personal life crisis", while the Der Spiegel newspaper said he had taken a break in training because of "burnout syndrome".
Outlining evidence from the crashed plane's black box cockpit voice recorder, Marseille prosecutor Brice Robin said Lubitz had deliberately put the plane into a descent after the captain left the cockpit.
He had refused to allow him back in and had made no response to calls from the ground or from other planes.
In his startling account of the doomed plane’s final half-hour, Mr Robin said: “I think the victims only realised at the last moment because on the recording we only hear the screams on the last moments of the recording.”
Some airlines are changing procedures to ensure two crew members are in the cockpit at all times during flights following the disaster.
The Australian government became the latest to impose such a requirement on Monday.
A father of one of the three British people on the flight called for more to be done to see pilots were "looked after", while the Observer said Civil Aviation Authority documents suggested some 100 commercial airline pilots in the UK had a history of depression, with 42 still on medication.
Philip Bramley, whose son Paul (28) was one of the three Britons on board the flight from Barcelona to Dusseldorf, said at the weekend: ”I believe the airlines should be more transparent and our finest pilots looked after properly. We put our lives and our children’s lives in their hands.”
PA