Jay Honeck wrote:

My mechanic -- a guy with over 40 years of experience as an IA, A&P,
grand champion home builder, and owner of an engine and prop shop --

Is he a pilot? airplane owner?

says it this way:

The average privately owned GA aircraft is flown AT MOST once a week.
As a result, rust (from inactivity) is the #1 killer of the average,
privately owned GA engine. Many don't make TBO because of
inactivity.

Touch & goes are the #1 worst thing you can do to your engine. Flight
school planes do them all day long, but it's because they are flown
daily, sometimes 8 hours per day, and they therefore NEVER experience
the ravages of inactivity. Therefore, although it's STILL the worst
thing you can do, the engines often make it to TBO simply because they
are flown all day, every day.

They make it to TBO because they are flown many hours per week, the
numbers add up fast, and they are monitored, inspected and maintained
every 100 hours (which might be every other month) ... not simply
because flying them every day enables the engine to withstand doing the
"worst" possible thing 75% of the time it is in use.

Engine out practice is essentially the same engine management
procedure as a touch & go. Long periods of high power, followed by
suddenly low RPM, followed by a sudden application of power at the
end.

And you do half of that every time you take off and land. That doesn't
damage your engine, but the one extra application of power during a
touch-n-go or go-around is going to do your engine in?

Bad, bad, bad.

Plenty of people practice touch-n-goes in their own airplanes ... if
they are THAT damaging to an engine, we'd be hearing of this engine
damage all the time. People with Cubs or other small tailwheels are out
doing touch-n-goes ALL THE TIME...doesn't seem to bother their engines.

I understand and agree about inactivity and that most privately-owned
airplanes aren't flown enough. But you're saying that an engine that
flies for 8 hours/month and does touch-n-goes/engine-out practice during
ONE of those hours is more likely to be damaged than an engine that
flies 80 hours a month and does the damaging maneuvers during 60 of
those hours. If it's THAT bad, subjecting it to 60 hours a month would
still take a heavy toll even it flies every day.

I've heard many owners and mechanics agree that the worst possible thing
you can do to an airplane engine is to NOT FLY IT; I've never heard
anyone say that privately owned airplanes aren't flown enough to do
touch-n-goes or simulated engine failures without risking damage to the
engine. In fact, wasn't part of your training getting so familiar with
the airplane that you know how it acts and reacts to as many different
conditions/configurations as possible? How can you do that if you're
afraid that touch-n-goes or simulated engine failures are going to ruin
the engine?

Are the engines designed to take this kind of abuse? Sure. But they
were designed to be run daily, not weekly, too.

I've never seen anything in my engine documentation that says it was
designed to be run every day.

And when you are
paying something in the range of $20,000 for an overhaul (as we did
for our O-540) we don't generally make a practice of stressing the
engine any more than necessary.

And as an airplane owner, that's your choice and your right.

I just spent at least that much, too, and I'm sure as heck not going to
intentionally abuse the engine. But I'm not going to skip some aspects
of ongoing skill retention drills that I've seen the pay off firsthand
in an emergency because I'm thinking about the $20K I just spent.

Maybe your reactions in a real engine emergency today would be just as
sharp and accurate as they were when you'd been practicing engine-outs
frequently in your private pilot training in school airplanes. I'm not
good enough to maintain that level of competence if I don't continue to
practice it every so often.

In skating, we used to teach students that they could expect to lose up
to 25% of their actual ability/competence during their 4 minute routine
in a competition due to nerves and pressure; so if they wanted to show
the judges 100% of their capabilities, they have to be skating at 125%
in the weeks prior to the competition. I don't know if those numbers
translate to flying, but I think the concept itself does. I would hate
to lose a percentage of my ability in an actual emergency if I was only
at 80% to begin with. YMMV, of course. Everyone's different.