AOPA Pilot Magazine - August 2023 - 76

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Which all leads to analysis. Despite monitors being
commonplace in the general aviation fleet for a few
decades now, we know very little about what a standard
profile should look like for each airplane and engine.
We know redlines. It's easy to look at the data and say
the engine oil was in the green or the CHTs didn't
exceed 400 degrees, but that's Little League stuff. What
good is it to have the data and be able to download it if
we can't tell what's normal and what's not?
Years ago Busch noticed that prior to an exhaust
valve failure there was a regular EGT oscillation of
about one cycle a minute. With some further sleuthing
he realized that was the rate at which the valve rotates,
so the temperature swing was the valve moving from the
hot side to the cold side. In 2011 Savvy Aviation released
a tool that finds that signature in a customer's data and
alerts him to the potential for a valve problem. I couldn't
help but notice our EGT line oscillated, but zooming in
on the platform it's a much smaller temperature swing
and a much more rapid change. Normal, I think.
Busch is hoping for more progress in the future.
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Savvy is in the midst of Project GADfly, or generalized
anomaly detection. The concept is simple. Take a
somewhat homogenous fleet (thank you, Cirrus) and
gather all its data. Map the complete data set over a
period of thousands of flights to establish what Busch
calls a hyperblob. Then build a profile of nearly every
parameter around that tightly clustered data set, and
eventually create analysis tools that alert owners when
one of their data points is outside the blob.
In one sense, Project GADfly is the answer to my
questions. I'll finally be able to know whether the
430-degree Fahrenheit gap in EGT at lower power
settings was really outside the norm or common behavior
for an IO-360-KB. But I can't help but wonder if it
really matters. I never worried about my exact EGT
prior to installing the engine monitor, and our engine
never had any serious problems. We were the proverbial
fat, dumb, and happy. But someone had looked at
our data, noted the large gap as a potential problem,
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An EGT probe delivers temperature data to a monitor on
the panel.
and we started looking for the culprit. A bad injector
was suspected. The mechanic measured the output
from each of the injectors and found them to be perfect.
We asked Continental, told them about the stumble
and sharp drop-off of the fuel flow from cylinder two
soon after takeoff on one flight, and followed their troubleshooting
steps. Without a clear answer they sent
The gap between the six cylinders seems alarming, but is actually quite good for a mid-1970s airplane. Gaps
of 50 degrees or more are common. Modern airplanes with better cooling efficiency see as little as 20 degrees
between cylinders.
76
AOPA PILOT / August 2023
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AOPA Pilot Magazine - August 2023

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