One of the worst cases of suicide but taking everyone on board as well was that German guy who flew his plane into a mountain on auto pilot with the rest of the crew unable to get back into the cock pit due to the 9/11 rules of not being able to force your way in.
Edit. I think it happened...
Mental health is a terrible thing for some people. I cant get my head around someone doing normal things like take the children to school, a dog walk, and a work call on the phone, then maybe on the spur of the moment decide to drown themselves. If that was indeed the case.