All in all i don't think this is easy one at all,,, you have people suffering from life issues/ mental conditions of various kinds which is not terribly uncommon i believe. Part of that set are possibly suicidal. And part of the suicidal ones are also capable of doing it while onboard a plane in the air. The last group must be very small. Now if the medical community are unable to accurately identify who belongs in the suicidal group accurately, how can anyone expect anyone else to identify the miniscule subset of that group. The ones that are capable of doing it in the air with people onboard.