Mechanical problems with the aircraft?
So he went mute as well and couldn’t respond to the pilot who was yelling and pounding on the door outside the cockpit?
There were no mechanical problems with the plane. He did it on purpose, because he was afraid to lose his pilot license if it came out that he had medical problems like a detached retina where he would lose his vision. He also had psychological problems, which he all hid from the company. The evidence was found by the German police in his house