Seriously, why? Can anyone think of a single justification?
The plane has a fully functioning communications suite, so if your plan was to commit suicide but then you got cold feet, you could call for help. Otherwise, what you’re looking at a best-case scenario in which you wind up sitting on a slowly-sinking aircraft for a little while until you wind up treading water until you drown or get eaten by sharks.
And you’d have six hours beforehand to do nothing but sit there and think about what lay in store.