#12: Germanwings Flight 9525 (2015)
On a flight from Barcelona to Düsseldorf, the Airbus A320 suddenly began a steady descent into the French Alps. Investigators later discovered the co-pilot had locked the captain out of the cockpit and deliberately crashed the plane, killing all 150 people onboard in an act of murder-suicide.

The case horrified the public and aviation industry alike. It led to immediate changes, including rules requiring at least two crew members in the cockpit at all times. Germanwings 9525 remains one of the darkest examples of how mental health and security concerns can collide in aviation.
