I believe and assume that the risk is somewhat akin to riding a motorcycle - i.e. considerably more dangerous than driving a car - although based on my attempts at getting life insurance, the typical life insurer thinks it is
more dangerous than that (a specialist sorted that one out). However, I think a major difference between flying and most other potentially-dangerous pursuits is that there are fairly few accidents that are totally outside your control - most can be either avoided by some sensible decision making or prepared for by training and currency. I would be interested to know how the "there but for the grace of god go I" accidents stack up against the ones that would earn you a page in "the Killing Zone", but I bet there are many more of the latter.
As to the measure of risk, god knows how the numbers are worked out, because we all know the issues with counting accidents per mile, per hour flown etc. Commercial air travel looks remarkably good when measured against driving the same distance, but less good per trip - and we all know that takeoff/landing is much more dangerous than the cruise. Lies, damn lies etc...
(edited for content, then spelling...
)