I know. But it need not be that hard - being suicidal does not automatically mean someone is prepared to e.g. fight their co-pilot to kill themselves. In fact, most people who are suicidal are not strongly intent on going through with it - it often takes just a little nudge one way or the other to change the outcome.

A co-pilot at the helm, or an unlocked door through which someone may come in and question the pilots actions could very well make all the difference.