Real stats on engine failures?

(Captain Wubba) writes:

So what is it? If the engine-failure rate is one failure for every
50,000 flight hours, I'll feel much less reticent about night/IFR
single-engine flying than if it is one in 10,000 hours. Anybody have
any facts or hard data, or have any idea where I might be able to
track some down?

Don't forget that you're safest with a single-cylinder engine. If
you have a six-cylinder, you're *six* times as likely to have a
failure.

....or at least that's what I've learned from some of the geniuses
who talk about twins vs. singles.

--kyler

"Kyler Laird" wrote in message
...
Don't forget that you're safest with a single-cylinder engine. If
you have a six-cylinder, you're *six* times as likely to have a
failure.

If the only thing that could go wrong with an engine was some sort of
failure of the cylinder, then that would actually be a pretty close
approximation of the truth. And in fact, if you have a six-cylinder engine,
you ARE (about) six times as likely to have a failure *of a cylinder* as you
would with a single-cylinder engine.

In the single vs. twin analysis, you have nearly double the chance of an
engine failure as with a single, all else being equal. If X (a number
between 0 and 1) is the chance of an engine failure for a single engine,
it's not that you have 2 * X chance of an engine failure for two engines.
You actually have 1 - ((1-X) * (1-X)) chance of an engine failure. But when
X is small (as it is in this case), the square of 1-X is pretty close to 1 -
(2 * X).

If all that could fail on an engine was a cylinder, or component related to
a cylinder, then a six-cylinder engine would be 1 - ((1-X) ^ 6) likely to
fail, where X is the chance of failure for a single-cylinder engine. But
just as 1 - ((1-X) ^ 2) is very close to 2 * X for small X, so too 1 -
((1-X) ^ 6) *is* actually very close to 6 * X for small X.

Now, with that essay out of the way, the real reason that six cylinder
engines aren't six times as likely to fail is that a number of failure modes
have nothing to do with the cylinder. They involve one or more other parts,
parts which exist in the same number regardless of the number of cylinders.

Note also that just as having two engines provides a benefit to offset the
very real increased opportunity for failure, having four, six, or more
cylinders provides a benefit to offset the very real increased opportunity
for *cylinder failure*. That is, with a six cylinder engine, if something
that IS specific to a cylinder fails, often the result is simply reduced
power, not a complete power failure.

...or at least that's what I've learned from some of the geniuses
who talk about twins vs. singles.

Sounds like you've got some good geniuses advising you. Stick with them.

Pete

"Kyler Laird" wrote in message
...
(Captain Wubba) writes:

So what is it? If the engine-failure rate is one failure for every
50,000 flight hours, I'll feel much less reticent about night/IFR
single-engine flying than if it is one in 10,000 hours. Anybody have
any facts or hard data, or have any idea where I might be able to
track some down?

Don't forget that you're safest with a single-cylinder engine. If
you have a six-cylinder, you're *six* times as likely to have a
failure.

...or at least that's what I've learned from some of the geniuses
who talk about twins vs. singles.

Not so, smart ass. You don't have six oil pumps, six crank seals, six fuel
pumps, six alternators, six crankshafts, 12 magnetos, 6 carbs, ect, ect, on
that six cylinder engine, do you?
--
Jim in NC

"Morgans" writes:

Don't forget that you're safest with a single-cylinder engine. If
you have a six-cylinder, you're *six* times as likely to have a
failure.

...or at least that's what I've learned from some of the geniuses
who talk about twins vs. singles.

Not so, smart ass. You don't have six oil pumps, six crank seals, six fuel
pumps, six alternators, six crankshafts, 12 magnetos, 6 carbs, ect, ect, on
that six cylinder engine, do you?

Correct, genius. Similarly, there are engine problems that are quite
independent of the number of engines on a plane.

--kyler

"Kyler Laird" wrote in message
...
Correct, genius. Similarly, there are engine problems that are quite
independent of the number of engines on a plane.

Such as? Other than fuel exhaustion, I'm at a loss to think of any.

"Peter Duniho" writes:

"Kyler Laird" wrote in message
...
Correct, genius. Similarly, there are engine problems that are quite
independent of the number of engines on a plane.

Such as? Other than fuel exhaustion, I'm at a loss to think of any.

Fuel exhaustion certainly accounts for a lot, but there's also
misfueling, fuel contamination, and intake clogging by widespread
particulates. All are as about likely to take out one as they are
several.

BTW, one of the things I like about a twin is the slight
difference in when such a loss is likely to happen. If one
engine runs out of fuel, runs into bad fuel, or gets socked with
ice/ash/..., at least I usually have a few seconds/minutes of power
on the other one before it experiences the same thing. It might
not seem like much, but it can be quite an advantage in sticky
situations. (Yes, yes...and if I decide to be stupid, it also
makes flipping the airplane over even easier - just like stalling a
single upon loss of power.)

--kyler

"Kyler Laird" wrote in message
...
Fuel exhaustion certainly accounts for a lot, but there's also
misfueling, fuel contamination, and intake clogging by widespread
particulates.

What's "misfueling"? Sounds like fuel exhaustion to me. As for the others,
you're right to the extent that all engines are run from the same fuel
supply. Many twins have separate tanks for each engine and may or may not
suffer the same problems.

In any case, the incidence of those failures is extremely low, compared to
the total number of failures (not counting fuel exhaustion of course which,
if I recall correctly, is the number one cause of engine failures).

The fact remains, having a second engine *does* significantly increase your
chances of an engine failure, just as having extra cylinders increases your
chance of having a cylinder failure. In most cases, it's a worthwhile
tradeoff, but one shouldn't pretend the tradeoff doesn't exist.

Pete

Peter Duniho wrote:

"Kyler Laird" wrote in message
...
Fuel exhaustion certainly accounts for a lot, but there's also
misfueling, fuel contamination, and intake clogging by widespread
particulates.

What's "misfueling"?

Putting jet-A in a gasoline burner (or vice-versa).

George Patterson
Some people think they hear a call to the priesthood when what they really
hear is a tiny voice whispering "It's indoor work with no heavy lifting".

"Peter Duniho" writes:

"Kyler Laird" wrote in message
...
Fuel exhaustion certainly accounts for a lot, but there's also
misfueling, fuel contamination, and intake clogging by widespread
particulates.

What's "misfueling"?

I was thinking of getting a fuel that will not burn effectively in
the plane's engine(s)

Sounds like fuel exhaustion to me.

I welcome suggestions on how I could have stated it more clearly.

As for the others,
you're right to the extent that all engines are run from the same fuel
supply.

Packing ice/ash/... into the _air_ intake has little to do with the
fuel supply. (Again, I think I was not clear.)

Many twins have separate tanks for each engine and may or may not
suffer the same problems.

If the lineman fuels the plane from the wrong (Jet A) truck, it's
unlikely to matter which tanks feed which engines unless you did
not fill all of the tanks.

In any case, the incidence of those failures is extremely low,

Great. I don't need to worry about all of those stories I heard of
getting JetA in an airplane marked "Turbo." Thanks.

The fact remains, having a second engine *does* significantly increase your
chances of an engine failure, just as having extra cylinders increases your
chance of having a cylinder failure. In most cases, it's a worthwhile
tradeoff, but one shouldn't pretend the tradeoff doesn't exist.

Agreed. I don't think anyone pretends the tradeoff doesn't exist.
Some do pretend that it is a linear relationship thus ignoring what
you describe as the most popular failures (along with the others
that I listed).

--kyler