No indication of co-pilot Andreas Lubitz's motives: Lufthansa chief

Carsten Spohr, chief executive of the German carrier, said he was "stunned" by findings that 28-year-old Andreas Lubitz appeared to have deliberately slammed the Airbus A320 into the French Alps.

All 150 people on board were killed in Tuesday's crash.

He told a news conference shortly after French officials gave an account of the flight's last minutes based on initial information gleaned from cockpit recordings that there was "no indication what might have led" to the young co-pilot's actions.

"In our worst nightmares we could not have imagined that this kind of tragedy could happen to us here at the company," Spohr said.

Cockpit employees are selected "very, very carefully" with much attention paid to their "psychological suitability", the Lufthansa chief, himself a former pilot, added.

Lubitz began his training in 2008 and six years ago had taken a break during the programme before resuming again. He had passed his medical, flying and other tests and checks.

A Lufthansa spokeswoman said he had 630 hours of flight experience.

"He was 100 percent airworthy, without reservation," Spohr said.

He added that no security "system in the world" could protect an airline from such a disaster.

"Whatever safety provisions you have in a company, however high the standards, such an isolated case cannot be completely ruled out," Spohr told reporters.