If the probability of an engine failing is 0.1, the probabilities for
all engines failing a

1 0.1
2 0.01
3 0.001
4 0.0001


5: not enough information to say. You do not specify that the probability of
an engine failing is independent of the other engines failing. Fly through a
volcano cloud and I bet you'll find that if one engine fails, the others will
too... quickly. Volcanos don't care about mathematics.


Things like ETOPS exist because the numbers say getting the probabilities
low is a good thing.


True enough. For independent failurs, get the "one engine" number down low
enough and the "two engine" number will also go down low enough. I'm sure they
also address dependent systems in ETOPS land too, and want a dependent failure
probability to be "low enough".

Jose


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