Co-pilot incapacitated or died, couldn’t open door
or
Plane intentionally flown into mountain.
Alps Crash Site ‘Freakishly Close’ to 1953 Disaster
On Sept. 1, 1953, an Air France Lockheed L-749A Constellation crashed into Mont Cimet, less than a mile away from the Germanwings site, as it prepared to land in Nice, NBC News reports.
http://www.newser.com/story/204494/alps-crash-site-freakishly-close-to-1953-disaster.html
Don’t they also had a Navagator in the cockpit.