After the shocking revelation that the Germanwings Airbus A320 that crashed in the Alps was apparently intentionally destroyed, one wonders how this could have happened. The problem seems to be that the lockable cockpit doors introduced to prevent terrorists taking over the cockpit can also enable an insider to lock out the crew. As such, it would be a good first step to implement the American rule that there must be always two people in a lockable cockpit worldwide. And as a second step we should take a hint from the protection of nuclear launch sites, and use two switches far enough apart that a single person cannot reach them simultaneously to confirm the cabin lock.
The design needs to prevent one person to lock out the crew, while staying robust against a takeover attempt by terrorists. A more concrete solution would be:
- The central lock switch remains, but only activates a one minute lock.
- To keep it locked for longer, both pilots need to confirm the lock simultaneously. This would be a switch each on the outer side, so that one person cannot reach both at the same time, and it would only trigger when a sensor registers the weight of the pilot in its seat.
- To be able to lock the door with only one active pilot, there is an emergency switch on the outside that triggers the lock, which can then be confirmed by a single pilot on the inside.