Thank you so much! I just have a question. Suppose P(A1) is probability of wing damage. P(A2) is probability of engine damage. You could say they are the same (but I think wings have larger area than engine and more likely to damage than engine so P(A1) is higher but it's OK to accept P(A1)=P(A2)=P(A). But how about P(B) successful return to base in two situations (1=wings damage 2=engine damage)? Is P(B1)=P(B2)=P(B)?