Hull losses are only a gross measure of safety. A hull loss may imply zero deaths, or 850 deaths.
Most air safety systems have automated or voluntary incident reporting. The incidents may have almost no safety implication by themselves (HUGE redundancy in a properly run airline), but are indicators of something that didn't go as planned or could otherwise be improved.
Based on these minutia, it is fairly straightforward to compute the propability of A+B+C+D all failing on a single flight, together presenting a genuine safety concern.
And you'd be amazed at how small the number is, compared to the risk of crossing the street.