Do not answer Mxsmanic

"Mxsmanic" wrote in message
...
Steve Foley writes:

Basic arithmetic is beyond you too?

1 + 1 = 2.

If the probability of any single engine failing is p, then the
probability of either of two engines failing is 1-(1-p)^2.


BZZZZZZZZZZZZTTT Wrong again stupid.

Try running your coin toss through this formula.

Tails = engine failure. 50% chance of failure.

Lemme know how you make out.

Steve Foley writes:

BZZZZZZZZZZZZTTT Wrong again stupid.

Try running your coin toss through this formula.

I did.

Chance of heads on one toss = 0.50

Chance of heads at least once on two tosses = 1-((1-0.50)*(1-0.50)) =
0.75

Chance of engine failure on single = 0.001

Chance of at least one engine failure with two engines =
1-((1-0.001)*(1-0.001)) = 0.001999

--
Transpose mxsmanic and gmail to reach me by e-mail.

On Thu, 12 Oct 2006 17:35:28 GMT, "Steve Foley"
wrote:

"Mxsmanic" wrote in message
.. .
Steve Foley writes:

Basic arithmetic is beyond you too?

1 + 1 = 2.

If the probability of any single engine failing is p, then the
probability of either of two engines failing is 1-(1-p)^2.


BZZZZZZZZZZZZTTT Wrong again...

Let's assume that the probability of an engine failure is an
astronomically high 0.1% or p=0.001. That means that the probability
of the engine not failing is p = 1 - 0.001 = 0.999.
There are 4 possibilities in the sample space, assuming that the
engine failures are independent, which they sometimes are not:

1. no engine fails. p = 0.999 * 0.999 = 0.998001
2. right engine fails p = 0.999 * 0.001 = 0.000999
3. left engine fails p = 0.001 * 0.999 = 0.000999
4. both engines fail p = 0.001 * 0.001 = 0.000001

Adding all these probabilities gives us a total of 1, showing that the
math is correct.

Adding all the probabilities of any kind of engine failure gives us
0.000999 + 0.000999 + 0.000001 = 0.001999

If the probability of engine failure in a single engine aircraft
remains 0.001, then 0.001999 / 0.001 = 1.999, or pretty darn close to
two. Twice the probability of a failure.

However, the case that we're most interested in is the probability of
both engines failing. The probability of that happening is 0.000001,
one thousandth the probability of total power failure in a single.

What this means is that if you fly a twin, you have roughly twice the
chance that you're going to have to use your diligently honed
engine-out skills than if you were flying a single. It also means that
if your engine-out skills are up to par and you can successfully cope
with an engine emergency, you'll have only one thousandth the chance
of a forced landing due to power failure. That's what you're buying
with the extra cost, fuel, and training. That and more load capacity,
speed, and looking cooler than anyone else on the ramp.

RK Henry

Recently, RK Henry posted:

However, the case that we're most interested in is the probability of
both engines failing. The probability of that happening is 0.000001,
one thousandth the probability of total power failure in a single.

What this means is that if you fly a twin, you have roughly twice the
chance that you're going to have to use your diligently honed
engine-out skills than if you were flying a single. It also means that
if your engine-out skills are up to par and you can successfully cope
with an engine emergency, you'll have only one thousandth the chance
of a forced landing due to power failure.

Well, I agree with your math up to your last point of there being only
..001 chance of a forced landing due to power failure because the data
doesn't support your conclusions.

Light twins with a single engine failure are sometimes forced to land, and
the percentage of those "landings" that are fatal is considerably higher
for twins than for singles (NTSB 2001 analysis: 27% vs. 17%), although a
higher percentage of the single engine fleet are involved in accidents
(.65% for twins vs. .88% for singles).

I'd surmise that if both engines failed, many critical decisions would be
made for you, and you could then concentrate on engine out skills or
forced landings that would increase the likelihood of survival.

http://www.ntsb.gov/publictn/2006/ARG0601.pdf

Neil

On Fri, 13 Oct 2006 17:26:19 GMT, "Neil Gould"
wrote:

Recently, RK Henry posted:

However, the case that we're most interested in is the probability of
both engines failing. The probability of that happening is 0.000001,
one thousandth the probability of total power failure in a single.

What this means is that if you fly a twin, you have roughly twice the
chance that you're going to have to use your diligently honed
engine-out skills than if you were flying a single. It also means that
if your engine-out skills are up to par and you can successfully cope
with an engine emergency, you'll have only one thousandth the chance
of a forced landing due to power failure.

Well, I agree with your math up to your last point of there being only
.001 chance of a forced landing due to power failure because the data
doesn't support your conclusions.

Light twins with a single engine failure are sometimes forced to land, and
the percentage of those "landings" that are fatal is considerably higher
for twins than for singles (NTSB 2001 analysis: 27% vs. 17%), although a
higher percentage of the single engine fleet are involved in accidents
(.65% for twins vs. .88% for singles).

I'd surmise that if both engines failed, many critical decisions would be
made for you, and you could then concentrate on engine out skills or
forced landings that would increase the likelihood of survival.

http://www.ntsb.gov/publictn/2006/ARG0601.pdf

Agreed. The analysis is a purely a priori probability model based on a
wild ass assumption. The real world, which is where most of us live,
is a lot more complicated. Many factors affect the outcome.

RK Henry

"Steve Foley" wrote in message
news:A1vXg.2851$lj2.2800@trndny01...
Basic arithmetic is beyond you too?

1 + 1 = 2.

If the probability of any single engine failing is p, then the
probability of either of two engines failing is 1-(1-p)^2.

BZZZZZZZZZZZZTTT Wrong again stupid.

Honestly...before you go around using insulting language, you really ought
to make sure you're not the one being stupid.

Try running your coin toss through this formula.

Tails = engine failure. 50% chance of failure.

Lemme know how you make out.

If you had done the same experiment, you'd have found that his formula is
correct. When the probability of an engine failure is 50%, then when one
engine, you have a 50% chance of failure, and with two engines you have a
75% chance of failure. That is, in fact, what his formula states.

So, to sum up, two things are correct in this thread:

* The chance of failure of any one of N items is not, strictly speaking,
the arithmetic sum of the chance of failure for one of those items alone.

* When the chance of failure is low, the actual chance of failure for
any one of those N items does turn out to be very close to the arithmetic
sum, even though that's not exactly the correct answer.

To any degree of precision relevant to a pilot, a twin has essentially twice
the chance of an engine failure that a single does. But it is true that it
is not *exactly* twice the chance of an engine failure.

Pete