PARIS/SEYNE-LES-ALPES - A young German co-pilot barricaded himself alone in the cockpit of Germanwings flight 9525 and apparently set it on course to crash into an Alpine mountain, killing all 150 people on board including himself, French prosecutors said on Thursday.
They offered no motive for why Andreas Lubitz, 27, would take the controls of the Airbus A320, lock the captain out of the cockpit and deliberately set it veering down from cruising altitude at 3,000 feet per minute.
The co-pilot had passed all the flight and medical tests and was "100 percent fit to fly", said Lufthansa chief executive Carsten Spohr on Thursday.
He said the co-pilot started his training in an aviation school in Bremen, Germany, in 2008, but interrupted for a while for reasons Spohr didn't mention.
The training then resumed, said Spohr, and he started to work as a co-pilot for Germanwings since 2013.
Police searched the co-pilot's home in Montabaur, Germany, leaving with large blue bags of evidence and a computer. A man was led out of the building, shielded by police holding up jackets.
The scenario stunned the aviation world. Within hours of the prosecutors' announcement, several airlines responded by immediately changing their rules to require a second crew member to be in the cockpit at all times. That is already compulsory in the United States but not in Europe.
Canada said it would now require it of all its airlines. EasyJet, Norwegian Air Shuttle and Air Berlin were among other carriers that swiftly announced such policies.
Among those that didn't was Germanwings parent company Lufthansa, whose CEO said he thought it was unnecessary. But the airline came under swift pressure on social media to make such a change and later said it would discuss it with others in the industry.
French and German officials said there was no indication Lubitz was a terrorist but offered no rival theories to explain his actions. Acquaintances described him as an affable young man who had given no sign of harmful intent.
Lubitz acted "for a reason we cannot fathom right now but which looks like intent to destroy this aircraft", Marseille prosecutor Brice Robin said.
