No offense meant to aircraft designers, my point is just that it's a common fallacy to assume that probabilistic events are independent when they are in fact de

No offense meant to aircraft designers, my point is just that it's a common fallacy to assume that probabilistic events are independent when they are in fact dependent in some ways. In the case of debris penetrating the tail, if one hydraulic line is severed, the probability of the other two also being severed is high, therefore the probability of a triple failure is not equal to p^-3; you must add to that the probability of this single catastrophic event occurring.