Sadly, if I applied Andy's rule, I'd probably have to give up my favourite subject, warbirds. I went through a bad spell a couple of years back when 3 or 4 aircraft crashed shortly after I'd photographed them - I was expecting pilots to have me banned from airshows.
Unfortunately, though, the chances are that if you photograph old aircraft, a high percentage are going to come to grief.
With regard to Andy's rule, mine is not photographing crashes, crash sites or wreckage.
Colin K. Work, Pixstel