About Germanwings flight 9525:

An Airbus A320 operated by Germanwings was destroyed in an accident in a mountainous area in southern France. All 144 passengers and six crew members were killed.
Flight 4U9525 departed Barcelona, Spain at 10:00 hours local time (09:00 UTC) on a regular passenger service to Düsseldorf, Germany. The flight reached its cruising altitude of FL380 at 10:27 hours. At 10:30 hours the flight was cleared direct to the IRMAR waypoint, which was confirmed by the flight: "Direct IRMAR, Merci 18G." This was the last radio contact with the flight.
At 10:30:08, the captain told the co-pilot that he was leaving the cockpit and asked him to take over radio communications, which the co-pilot acknowledged.
At 10:30:53, the selected altitude on the Flight Control Unit (FCU) changed in from 38,000 ft to 100 ft. One second later, the autopilot changed to OPEN DES mode and autothrust changed to THR IDLE mode. The airplane started to descend and both engines' speed decreased.
At 10:33:12, the speed management changed from managed mode to selected mode. One second later, the selected target speed became 308 kt while the aeroplane's speed was 273 kt. The aeroplane's speed started to increase along with the descent rate, which subsequently varied between 1,700 ft/min and 5,000 ft/min, then was on average about 3,500 ft/min.
The selected speed decreased to 288 kt. Then, over the following 13 seconds, the value of this target speed changed six times until it reached 302 kt.
At 10:33:47, the controller asked the flight crew what cruise level they were cleared for. The airplane was then at an altitude of 30,000 ft in descent. There was no answer from the co-pilot. Over the following 30 seconds, the controller tried to contact the flight crew again on two occasions, without any answer.
Thereafter the selected speed increased up to 323 kt. Then the buzzer to request access to the cockpit sounded, but the copilot did not react.
Marseille control centre kept attempting to contact the flight, without any response.
The selected speed was again increased, this time to 350 kt. Meanwhile the captain attempted to call the copilot over the interphone and there were noises similar to a person knocking on the cockpit door.
At the same time Marseille control and a controller from the French Air Defence system called the flight at various frequencies, without success.
As the aircraft kept descending noises similar to violent blows on the cockpit door were recorded on five occasions between 10:39:30 and 10:40:28.
The GPWS then sounded: "Terrain, Terrain, Pull Up, Pull Up" until the aircraft impacted a sloping rocky ravine in mountainous terrain at an elevation of 1550 meters.

Probably cause:

The collision with the ground was due to the deliberate and planned action of the co-pilot who decided to commit suicide while alone in the cockpit. The process for medical certification of pilots, in particular self-reporting in case of decrease in medical fitness between two periodic medical evaluations, did not succeed in preventing the co-pilot, who was experiencing mental disorder with psychotic symptoms, from exercising the privilege of his licence.
The following factors may have contributed to the failure of this principle:
- the co-pilot's probable fear of losing his ability to fly as a professional pilot if he had reported his decrease in medical fitness to an AME;
- the potential financial consequences generated by the lack of specific insurance covering the risks of loss of income in case of unfitness to fly;
- the lack of clear guidelines in German regulations on when a threat to public safety outweighs the requirements of medical confidentiality.

Security requirements led to cockpit doors designed to resist forcible intrusion by unauthorized persons. This made it impossible to enter the flight compartment before the aircraft impacted the terrain in the French Alps.