It took criminal investigators less than 48 hr. to determine the likely cause of the Germanwings Flight 9525 disaster. They say they are certain the first officer “deliberately crashed” the Airbus A320 into the side of a mountain, an event that will raise questions about psychological oversight of pilots and cockpit access.

Brice Robin, the Marseille-based criminal prosecutor in charge of the case, revealed the conclusions at a March 26 briefing. Robin, who has had full access to the audio file found on the cockpit voice recorder recovered only hours after the crash, revealed evidence that he believes proves the first officer was alone on the flight deck, alive, and not incapacitated during the flight’s fatal descent.

Robin works independently of and in parallel with the French air accident investigation bureau. He bases his conclusion on a number of factors, leading with the first officer not allowing the captain back into the cockpit, followed by a controlled descent that seems consistent with a deliberate act.

If Robin’s theory is confirmed, the industry could be facing a debate as to whether introduction of secure cockpit doors, initiated after the 9/11 terrorist attacks in the U.S., has created a safety issue in and of itself.

The A320 cockpit door can be opened from outside using an emergency code entered into a keypad. At Lufthansa and Germanwings, pilots and cabin crew are aware of the code. Once entered, the door can be opened from outside after about 30 sec., but this can be overridden from inside the cockpit by moving the door button to the locked position. The first officer could have used this device to ensure his plan was carried out.

There are now at least four crashes since 1994 that investigators believe can likely be attributed to deliberate pilot action. The Linhas Aereas de Mocambique (LAM) Embraer 190 crash in November 2013 mirrors the Germanwings’ sequence of events. 

Deliberate action by pilots is also one of the theories behind the disappearance of Malaysia Airlines Flight 370.  

The circumstances surrounding the demise of Flight 4U 9525 also raise the question of mandating regular psychological checks in tandem with annual medical checks for pilots, and have opened debates into other procedures to help pinpoint suicide-prone crew. 

Processes vary from airline to airline. In the Lufthansa Group, pilots are examined by psychologists when they are selected, but there are no further checks. An informal system is in place in which colleagues can file comments or complaints in case of unusual behavior, but company insiders say these channels are rarely used.

EasyJet and Norwegian Air Shuttle are the first European airlines to revise cockpit procedure. They now require two crewmembers in the cockpit at all times. If one pilot exits, he must be replaced by a relief pilot or cabin crew member.

The aircraft took off as Flight 4U 9525 from Barcelona at 10:01 a.m. -local time on March 24. The aircraft reached its cruising altitude of 38,000 ft. at 10:27. Its last air traffic control (ATC) contact took place at 10:30 a.m. and was a routine communication which cleared the aircraft for the IRMAR waypoint around 25 nm south of Barcelonnette, France. One minute later the aircraft began its unexpected descent, losing approximately 30,000 ft. in altitude in 8 min.—a relatively steep drop, but well within the aircraft’s normal flight envelope. The last recorded altitude was 6,175 ft., slightly higher than where the aircraft crashed into a mountain. All 150 people onboard died.

The 28-year-old first officer, Andreas Lubitz, had only 630 airline flight hours. He was trained by Lufthansa and began flying as a first officer on the A320 family in September 2013. According to Spohr, Lubitz had to interrupt his training for several months. Reasons for the interruption were not given, but industry sources say they were “medical.” He had no issues during his time as a line pilot, the sources add.

Robin confirmed that the two pilots conducted a normal, cordial conversation before the captain left the cockpit to use the lavatory. The European Aviation Safety Agency allows one pilot to leave the cockpit for operational or “physiological” reasons. The first officer did not speak after the captain left. Knocking and banging on the cockpit door—presumably from the captain seeking to regain access to the flight deck—is audible on the cockpit voice recorder. The escalating noise also leads the prosecutor to believe that the captain and others tried to smash the door with force.

ATC made several attempts to contact Flight 4U 9525, to no avail; the aircraft’s transponder code had not been switched to emergency mode. Other aircraft in the area also tried to contact the doomed Germanwings A320.

Robin said the recording picked up normal breathing by the first officer as well as screams from the cabin in the flight’s final moments. He has effectively ruled out terrorism. Criminal probes of fatal aircraft accidents are commonplace in France, and Robin’s involvement started before any evidence of a crime came to light.