> In response to the incident and the circumstances of the co-pilot's involvement, aviation authorities in some countries implemented new regulations that require the presence of two authorised personnel in the cockpit at all times. Three days after the incident, the European Aviation Safety Agency issued a temporary recommendation for airlines to ensure that at least two crew members—including at least one pilot—were in the cockpit for the entire duration of the flight. Several airlines announced that they had already adopted similar policies voluntarily. But by 2016, the EASA stopped recommending the two-person rule, instead advising airlines to perform a risk assessment and decide for themselves whether to implement it. Germanwings and other German airlines dropped the procedure in 2017.

I guess the underlying assumption is that the regular medical tests that pilots are subjected to should keep pilots capable of mass murder-suicide out of a cockpit. Indeed, Lubitz had been declared "unfit for work" by a doctor, but apparently the doctor trusted Lubitz himself to pass this on to his employer, because "medical secrecy requirements prevented his physician from making this information available to Germanwings".