Upvote:5
deaths per passenger mile
If you are looking at "safety", that's actually the wrong metric. People do die on airplanes and boats but the majority of these fatalities have natural causes.
If you look at accidental death's only, the numbers are really too small to make any meaningful statistical comparison. In the 5 years from 2014-2018 there was a total of 1 accident related fatality in all US domestic flights. source
A larger number of accidental deaths often occurs in a single event, which are extremely rare. This makes statistics even more meaningless. It just boils down to something like this:
Both means of transportation are quite safe.