AOPA Pilot Magazine - November 2021 - 85

operational factors. A prop that lives in
Tucson, Arizona, can remain corrosionfree
much longer than one that lives in
Tampa, Florida, and one that lives in a hangar
will go a lot longer than one that lives on
a tiedown. Also, a prop that flies 10 hours a
month throughout the year will remain corrosion-free
much longer than one that flies
20 hours a month in the summer and sits
unflown in the winter (or vice versa).
None of these factors are considered
in the one-size-fits-all TBOs that
the manufacturers specify. In fact, manufacturers
base their TBOs on worst-case
assumptions to ensure they are appropriate
for even the worst-case airplane in the
fleet-you know, the one that sits out on
a tiedown in Tampa just spitball distance
from the Gulf of Mexico and only flies six
months out of the year. This makes those
TBOs inappropriately short for most of the
fleet, especially the ones that are hangared
in Tucson and fly regularly year-round.
A common-sense approach
That's why I recommend you adjust manufacturer-specified
TBOs-particularly
the calendar-time component-to fit your
individual situation. If your airplane is tied
down in an area of high corrosion risk-
near the coast or the Gulf-perhaps you
should comply with the 60- or 72-month
schedule recommended by the prop manufacturer.
If you're based in an area of
only moderate corrosion risk, you might
reasonably go twice as long. If you're
lucky enough to be based somewhere like
Tucson or Denver or Missoula where corrosion
is banned by local statute, you could
go triple. Give yourself extra credit if your
airplane is almost always hangared, and
ding yourself if your operation is seasonal
or irregular.
Lest you conclude this advice is dangerous
heresy, I will tell you that some
years ago I had the opportunity to have a
one-on-one conversation with the head
of product support for one of the major
propeller manufacturers. I told him my
thoughts about individualizing prop TBO
along the lines I just described. " I can't
find fault with your thoughtful approach, "
he confided, " but if you tell anyone I said
that, I'd probably get in seriously hot
water with our legal department. "
The hub of a constant-speed prop contains stuff that your IA cannot inspect. A reseal repair is the
most economical way to deal with that.
Interestingly, there's one prop manufacturer-Sensenich-that
has dropped
all calendar-time recommendations on
its propellers and quotes TBOs strictly
in terms of operating hours. In fairness,
however, I should point out that
Sensenich makes only fixed-pitch props
and that corrosion is much more of a concern
with constant-speed props because
it may be hidden inside the propeller hub.
I'm not holding my breath for Hartzell,
McCauley, or MT to follow Sensenich's
lead on this.
The half-price overhaul
The FAA allows A&P mechanics to work
on virtually every component of an aircraft
with two specific exceptions: propellers
and instruments. Propeller repairs (anything
beyond dressing small nicks and
painting blade tips) must be done by an
FAA-certified propeller repair station,
and instrument repairs (anything beyond
removal and installation) must be done by
an FAA-certified instrument repair station.
Consequently, most A&Ps know very
little about propellers and instruments.
Soon after I became an A&P, I made a
point of trying to fill this knowledge vacuum
by visiting instrument shops and
prop shops every chance I got. In March
1996, I had both of my Cessna 310's propellers
overhauled by American Propeller
Service in Redding, California, and I got
permission to spend the week hanging out
at the prop shop while my props and dozens
of others were being worked on. That
was quite a learning experience.
One thing I noticed was that while
most of the propellers were coming into
the shop for overhauls, some were coming
in for something called a " reseal repair "
(sometimes called a " clean and seal " ). I
asked shop foreman Todd Marinkovich
what the difference was between an overhaul
and a reseal repair, and he explained
that a reseal repair was basically an overhaul
of the prop hub only, with the blades
left alone. In contrast, a full overhaul
involves stripping the blades of paint and
deicing boots, putting them through fluorescent
dye inspection, measuring the
chord and twist at numerous stations
along the length of the blade, performing
any necessary trimming or twisting, and
finally repainting the blades and installing
new deicers if applicable. That's a lot
of labor, which is why a reseal repair typically
costs half or less what an overhaul
will cost.
AOPA PILOT / November 2021
85

AOPA Pilot Magazine - November 2021

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