Well, yesterday I would not have believed it possible, but it would appear that we have a suicide by the First Officer.
We will now be faced with the usual call for "something" to be done.
But what? Eventually this is a matter of trust which we have to have in people.
A train driver, bus driver, surgeon, ship captain, the list goes on forever of people who individually hold our lives in their hands.
Even with an extra member of staff on the flight deck an a/c can be crashed on purpose in moments.
Who is going to prevent me suddenly stamping sudden full rudder at m0.81?
Is a flight attendant going to stop me switching off the flight control computers and applying full forward side stick?
Of course, the answer is no,
Trust is indeed the only answer to this problem. There have been train drivers who have failed to stop at terminus stations and ultimately investigators have not be able to come to any other conclusion than driver suicide. The Moorgate incident on the London Underground springs to mind. But thankfully, despite the opportunity presented to solo drivers throughout the subways of the world, it seems their minds don't generally follow the same dark labyrinths that their train full of passengers do. We have to trust them.
I think we have to accept that suicide cant be stopped, mainly because we rarely know it is going to happen. But, changing all the rules everytime an event like this occurs is probably not the answer either. So, leave the security doors in place, ensure there are two on the FD at all times, don't substitute intelligent pilots for unintelligent computers and don't overplay the state of mind issues during medicals.
What airlines could do is ensure that all employees flying and non flying have easy access, without prejudice to caring, confidential and non-judgmental support services for staff who feel they need help. Does your airline already have that?