The issue, conveniently forgotten by AnFI
- not at all.
Because
... mathematically speaking!
It is
not correct or relevant to use
the probability of one failure followed by a second from an unconnected cause ('a' followed by 'b') is 1 x 10**-10.
Lookup Sir Roy Meadows and what the Royal Statistical Society thought of the use of the same statistic.
Jim - what figure would you put on 'a' following 'b'?
is it in the order of 1in10?
rather than 1 in 100,000?
Would you also agree with me that it's not the risk of forced landing through the 'engine failure' cause but
any cause which needs to be factored in?
So:
The other risks from having 2 engines should also be factored in. ie:
the risk of running a complex gearbox (Rgb)
the risk from running all the critical components to a higher load than would be
the risk of major destructive Eng failure etc.
The accidents we see, demonstrate that 1x10^-10 is not relevant.
Also the 'fatalness' of the hostile environment needs attention. You are using the consequence of failure in a hostile area as P=1 , all I was pointing out is that
the consequences need to be much worse than this to justify the unreliability of two engines.... mathematically speaking
Risk of death in ditching in GOM? 0.1? 0.01?
it is mathematically speaking much easier to do something about that sized number than a number already this small - 0.0000001
People are generally not good at estimating risk.
Do you carry a knife when you carry a dingy in the cockpit?