In article ,
"Peter Duniho" wrote:

"Ron Garret" wrote in message
...
[...]
and have determined the number of trials (flights) in advance.

No. That statement is true regardless of whether N is known.

Knowing that your chances of having an engine failure are 1-(1-P)^N isn't
very useful information if you don't know what N is.

As I pointed out before (and will point out again later on -- watch for
it) it is useful because you can choose your risk tolerance and then
solve for N (assuming of course you know P).

It's not a useful calculation for the purpose of this discussion.

That is a matter of opinion.

Tell me how I'm going to use the information then. Since you think it's so
useful.

I just did, but here it is again: if you believe that the risk of an
engine failure on any particular flight is P1 and you are willing to
accept a lifetime risk of experiencing an engine failure at no more than
P2, then you can use these two numbers and the formula for cumulative
probability to solve for N. You can then choose to stop flying after N
flights.

No one knows before they've started flying how many flights they will
make
in a lifetime.

That is not necessarily true. My mother, for example, knows exactly how
many flights in GA aircraft she will make during her lifetime: zero.

For a person who will never make a flight in a GA aircraft, why in the world
would I consider at all how many engine failures she'll experience?

It's like trying to figure out how many live births I'll have in my
lifetime. Duh.

No, because in my mother's case the number is zero because she has
*chosen* to make it zero. (Perhaps I should have made it clear that I
am a pilot, and so my mother can, if she chooses, go flying with me any
time she wants.) Your analogy is faulty because you cannot choose to
get pregnant.

And just in case you're too dimwitted to extrapolate from this example
I'll spell it out for you: one can *decide* on the basis of this
calculation to stop flying after some number of flight because flying
more than that results in a cumulative probability of disaster that
exceeds one's risk tolerance.

Only if they make that decision prior to flying those hours. I haven't met
a single person who has ever done such an analysis of their flying career.
I doubt one exists.

Just because you are not personally acquainted with someone who has
chosen to avail themselves of the utility of this calculation does not
mean that such people do not exist. (And even if it were true that no
one in the world has availed themselves of this utility (which it isn't)
that would not prove that the calculation is without utility.)

If you can find me one, I'll stand corrected.

I very much doubt that. You seem not to have noticed, but we've
actually already done that experiment, and you stubbornly cling to your
position regardless.

Not only are you wrong, but you are clearly, demonstrably, and
self-evidently wrong. If you don't believe me, you can actually *do*
this experiment. Don't play the lottery or go flying until your engine
fails. Get a die. Pretend that rolling a six means your engine has
failed. Now ask yourself: are you more likely to roll a six if you roll
it once, or if you roll it 100 times? Clearly if you roll it once your
chances are one in six, and if you roll it 100 times the chances of
rolling AT LEAST ONE SIX in those hundred trials is very close to 1.
(0.99999998792532652 to be precise).

Otherwise, you are without a point

Whereas you seem to have one on the top of your head.

(I'll refrain from any implication that YOU are dimwitted, just 'cause
that's the kind of guy I am).

Hey, if the shoe fits, I'll wear it. Will you?

rg