It is generally bad luck to view the belly of a heavy bomber as it passes overhead.

I had an interesting exchange with a senior engineer at Boeing, where we all honored and praised the venerable B-17 as a matter of course. "Unlike everyone else, I don't have a good opinion of the B-17." Oh, really? "Yes. I saw too many of them in action...from underneath." He was a German immigrant and, as a boy, suffered allied bombardment during World War 2.