AOPA Pilot Magazine - May 2017 - 87

If you have one of these...you could
Plug 'N Play with one of these!
differential compression test. A compression test could tell you that air was leaking
past the exhaust valve, but with the borescope you could tell whether it was because
of a benign glob of lead on the seat that
would quickly resolve itself the next time
the engine ran-or a malignant, warped or
eroded valve likely to fail catastrophically
in the next 10 hours. How cool was that?
Over the years, the compression test
has proved untrustworthy and prone
to false positives, resulting in tens of
thousands of cylinders being removed
unnecessarily (including a few of mine).
That's why the SB03-3 guidance calls for
any disqualifying compression test that is
not corroborated by borescope evidence
be retested after flying for at least 45 minutes. That's excellent advice. I've seen
many cases where a cylinder that flunked
the first compression test easily passed the
second one. In one notable case involving a
Cirrus SR22, a cylinder that tested at 38/80
(and that the shop doing the annual wanted
to yank) wound up measuring 72/80 on the
retest after a one-hour flight.
SB03-3 did not go so far as to recommend
that borescope inspections should replace
the venerable compression test. Continental
couldn't do that, because the requirement to
perform a compression test is written into
the FARs (Part 43, Appendix D). But SB03-3
did all it could to convey that Continental is
no big fan of the compression test for determining cylinder airworthiness. (A senior
Continental executive once confessed to me
that if they could've dropped the compression test altogether, they would have.)
I consider SB03-3 to be the best thing
ever written on the subject of how to decide
whether a cylinder needs to come off. It has
saved owners of Continental engines millions of dollars in maintenance costs. In my
view, it's high time that Lycoming followed
suit and revised its archaic guidance on the
subject. (Last year, Continental incorporated the contents of SB03-3 into its new
Standard Practice Maintenance Manual
M-0, so it no longer exists as a separate service bulletin.)
TODAY'S SCOPES: WOW!

In the computer industry, Moore's Law
(named after Intel co-founder Gordon
www.aopa.org/pilot AOPA PILOT | 87

Bendix/King KMA-28

GARMIN GMA340

UPS-AT SL-15

PMA8000B or PMA8000BT with Bluetooth®
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PMA8000G with flightmate®

PMA7000B and PMA7000BT
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GRAVITY
OUTSMARTED.

Cruise Comfortably Under Power to the
Best Soaring Sites in America

WES CHUMLEY

803.726.8884 * info@stemme.com
stemme.com
http://www.PS-Engineering.com http://www.stemme.com http://www.aopa.org/pilot
Table of Contents for the Digital Edition of AOPA Pilot Magazine - May 2017
