Danny42C,
Mathematically, '(b)' must be true. Yet the trouble was that some roulette wheels seemed to have memories, in which case the odds on the 'chop' on your last trip could be 3x30 = 90%, as you suggest.
Assuming that the chance of being shot down on any single sortie remains a constant 3%, the mathematics of probability dictate that the likelihood of surviving 30 consecutive sorties is 0.97^30, which works out at 40%. This is pretty close to the observed figure of 50%. Reverse-engineering that 50% (by taking the 30th root of 0.5) indicates an average single-sortie loss rate of 2.3%.
Sorry, don't have any useful observations on that, but thought the mathematical input would at least be of interest!