AOPA Pilot Magazine - November 2021 - 84

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This Hartzell service letter sure tries hard to convey the notion that overhauling props and governors
at TBO is compulsory, but it isn't.
The FAA dictates certain inspection
and maintenance intervals through Part
91 regulations. Notably, FAR 91.409(a)
says that we're required to perform annual
inspections every 12 calendar months;
91.409(b) says that we're also required
to perform 100-hour inspections if we
use our aircraft to carry passengers or
give flight instruction for hire; 91.207(d)
requires annual emergency locator transmitter
inspections; and 91.411 and 413
require biennial certifications of transponders,
altimeters, and altitude encoders.
Between these FAA-mandated inspections,
FAR 91.405 requires us to have
discrepancies repaired, maintenance
work logged and signed off, and inoperative
equipment placarded. FAR 91.403
makes us responsible for complying with
all applicable airworthiness directives and
airworthiness limitations.
With respect to propellers, there are a
tiny handful of ADs and airworthiness limitations
that dictate TBOs or component
life limits for a few very old propellers
and a few oddball airframe/engine/propeller
combinations (mostly involving
turboprops). For the vast majority of us,
however, the FAA leaves the when-tooverhaul
decision totally up to the Part 91
owner/operator.
84
AOPA PILOT / November 2021
Why prop TBO is what it is
How can an aircraft owner make an
informed decision about when to overhaul?
I think a useful place to start is to
look at how aircraft propeller manufacturers
like Hartzell, McCauley, MT, and
Sensenich come up with their TBO recommendations
in the first place.
Why, for example, do the manufacturers
define TBO in terms of both operating
hours and calendar months? It's because
they're concerned not only about wear
and metal fatigue (which correlates
directly with operating hours) but also
about corrosion and seal deterioration
(which correlates directly with calendar
time and inactivity). The theory is that
by defining TBO in terms of both hours
and months, high-activity props will get
overhauled before they wear out and lowactivity
props will get overhauled before
they corrode excessively.
Now, that's a nice theory but it misses
some important factors that should influence
how often prop overhauls are done.
Ask any prop shop what the most serious
problem they see when they disassemble
propellers for overhaul, and they'll all
give you the same answer: corrosion. But,
when it comes to corrosion, calendar time
is less important than environmental and

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AOPA Pilot Magazine - November 2021

Table of Contents for the Digital Edition of AOPA Pilot Magazine - November 2021

Contents
AOPA Pilot Magazine - November 2021 - Intro
AOPA Pilot Magazine - November 2021 - BB1
AOPA Pilot Magazine - November 2021 - BB2
AOPA Pilot Magazine - November 2021 - Cover1
AOPA Pilot Magazine - November 2021 - Cover2
AOPA Pilot Magazine - November 2021 - Contents
AOPA Pilot Magazine - November 2021 - 2
AOPA Pilot Magazine - November 2021 - 3
AOPA Pilot Magazine - November 2021 - 4
AOPA Pilot Magazine - November 2021 - 5
AOPA Pilot Magazine - November 2021 - 6
AOPA Pilot Magazine - November 2021 - 7
AOPA Pilot Magazine - November 2021 - 8
AOPA Pilot Magazine - November 2021 - 9
AOPA Pilot Magazine - November 2021 - 10
AOPA Pilot Magazine - November 2021 - 11
AOPA Pilot Magazine - November 2021 - 12
AOPA Pilot Magazine - November 2021 - 13
AOPA Pilot Magazine - November 2021 - 14
AOPA Pilot Magazine - November 2021 - 15
AOPA Pilot Magazine - November 2021 - 16
AOPA Pilot Magazine - November 2021 - 17
AOPA Pilot Magazine - November 2021 - 18
AOPA Pilot Magazine - November 2021 - 19
AOPA Pilot Magazine - November 2021 - 20
AOPA Pilot Magazine - November 2021 - 21
AOPA Pilot Magazine - November 2021 - 22
AOPA Pilot Magazine - November 2021 - 23
AOPA Pilot Magazine - November 2021 - 24
AOPA Pilot Magazine - November 2021 - 25
AOPA Pilot Magazine - November 2021 - 26
AOPA Pilot Magazine - November 2021 - 27
AOPA Pilot Magazine - November 2021 - 28
AOPA Pilot Magazine - November 2021 - 29
AOPA Pilot Magazine - November 2021 - 30
AOPA Pilot Magazine - November 2021 - 31
AOPA Pilot Magazine - November 2021 - 32
AOPA Pilot Magazine - November 2021 - 33
AOPA Pilot Magazine - November 2021 - 34
AOPA Pilot Magazine - November 2021 - 35
AOPA Pilot Magazine - November 2021 - 36
AOPA Pilot Magazine - November 2021 - 37
AOPA Pilot Magazine - November 2021 - 38
AOPA Pilot Magazine - November 2021 - 39
AOPA Pilot Magazine - November 2021 - 40
AOPA Pilot Magazine - November 2021 - 41
AOPA Pilot Magazine - November 2021 - 42
AOPA Pilot Magazine - November 2021 - 43
AOPA Pilot Magazine - November 2021 - 44
AOPA Pilot Magazine - November 2021 - 45
AOPA Pilot Magazine - November 2021 - 46
AOPA Pilot Magazine - November 2021 - 47
AOPA Pilot Magazine - November 2021 - 48
AOPA Pilot Magazine - November 2021 - 49
AOPA Pilot Magazine - November 2021 - 50
AOPA Pilot Magazine - November 2021 - 51
AOPA Pilot Magazine - November 2021 - 52
AOPA Pilot Magazine - November 2021 - 53
AOPA Pilot Magazine - November 2021 - 54
AOPA Pilot Magazine - November 2021 - 55
AOPA Pilot Magazine - November 2021 - 56
AOPA Pilot Magazine - November 2021 - 57
AOPA Pilot Magazine - November 2021 - 58
AOPA Pilot Magazine - November 2021 - 59
AOPA Pilot Magazine - November 2021 - 60
AOPA Pilot Magazine - November 2021 - 61
AOPA Pilot Magazine - November 2021 - 62
AOPA Pilot Magazine - November 2021 - 63
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AOPA Pilot Magazine - November 2021 - 65
AOPA Pilot Magazine - November 2021 - 66
AOPA Pilot Magazine - November 2021 - 67
AOPA Pilot Magazine - November 2021 - 68
AOPA Pilot Magazine - November 2021 - 69
AOPA Pilot Magazine - November 2021 - 70
AOPA Pilot Magazine - November 2021 - 71
AOPA Pilot Magazine - November 2021 - 72
AOPA Pilot Magazine - November 2021 - 73
AOPA Pilot Magazine - November 2021 - 74
AOPA Pilot Magazine - November 2021 - 75
AOPA Pilot Magazine - November 2021 - 76
AOPA Pilot Magazine - November 2021 - 77
AOPA Pilot Magazine - November 2021 - 78
AOPA Pilot Magazine - November 2021 - 79
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AOPA Pilot Magazine - November 2021 - 81
AOPA Pilot Magazine - November 2021 - 82
AOPA Pilot Magazine - November 2021 - 83
AOPA Pilot Magazine - November 2021 - 84
AOPA Pilot Magazine - November 2021 - 85
AOPA Pilot Magazine - November 2021 - 86
AOPA Pilot Magazine - November 2021 - 87
AOPA Pilot Magazine - November 2021 - 88
AOPA Pilot Magazine - November 2021 - 89
AOPA Pilot Magazine - November 2021 - 90
AOPA Pilot Magazine - November 2021 - 91
AOPA Pilot Magazine - November 2021 - 92
AOPA Pilot Magazine - November 2021 - 93
AOPA Pilot Magazine - November 2021 - 94
AOPA Pilot Magazine - November 2021 - 95
AOPA Pilot Magazine - November 2021 - 96
AOPA Pilot Magazine - November 2021 - 97
AOPA Pilot Magazine - November 2021 - 98
AOPA Pilot Magazine - November 2021 - 99
AOPA Pilot Magazine - November 2021 - 100
AOPA Pilot Magazine - November 2021 - 101
AOPA Pilot Magazine - November 2021 - 102
AOPA Pilot Magazine - November 2021 - 103
AOPA Pilot Magazine - November 2021 - 104
AOPA Pilot Magazine - November 2021 - 105
AOPA Pilot Magazine - November 2021 - 106
AOPA Pilot Magazine - November 2021 - 107
AOPA Pilot Magazine - November 2021 - 108
AOPA Pilot Magazine - November 2021 - 109
AOPA Pilot Magazine - November 2021 - 110
AOPA Pilot Magazine - November 2021 - 111
AOPA Pilot Magazine - November 2021 - 112
AOPA Pilot Magazine - November 2021 - Cover3
AOPA Pilot Magazine - November 2021 - Cover4
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