AOPA Pilot Magazine - January 2025 - 87

" Expect a callback within 15 minutes, "
the operator told Annecchini.
About 10 minutes later, Savvy's on-call
account manager, A&P/IA Tom Cooper,
called Annecchini back, but the call rolled
to voicemail so Cooper left a message.
While waiting for Annecchini to call
him back, Cooper brought another Savvy
account manager, A&P/IA James Watson,
onto Annecchini's ticket. Watson owns and
operates Watson Aero LLC in Louisville,
Georgia, a superb aircraft engine overhaul
shop, and serves as one of several engine
specialists on Savvy's technical team.
Watson reached Annecchini via
cellphone. He went over all the information
on Annecchini's ticket, asked some
questions, and learned that Annecchini's
61-year-old airplane was equipped
with a very modern and capable digital
engine monitor, an Electronics
International CGR-30P.
Differential diagnosis
Watson knew that modern digital engine
monitors like the CGR-30P are usually
extremely accurate. Yet the oil temperature
readings that Annecchini was reporting
were highly suspect. If the oil was at 330
degrees or 340 degrees, it would be caramelized
and look dark and smell awful. But
Annecchini had checked the dipstick and
found the oil looked and smelled normal.
The cylinder head temperatures
Annecchini was reporting in the 420
degree and 440 degree range would have
been abnormally high but possible had the
airplane been at full takeoff power-CHT
redline for the Continental O-470-R is
460 degrees-but 440 degrees was clearly
impossible with the engine at taxi power,
and 420 degrees was even more impossible
with the engine shut down.
When an instrument reading violates
the laws of physics, it has to be wrong.
Clearly, Annecchini's fancy digital engine
monitor was lying to him. But why?
If the engine monitor was displaying
just one or two temperatures that were
crazy, the problem might have been a bad
oil temperature or CHT probe, although the
thermocouple probes used by most modern
engine monitors almost always fail in the
low direction, not the high direction. But
Annecchini was quite certain that all six
CHTs were showing 420 degrees or higher,
and he was pretty sure that all the exhaust
gas temperatures looked higher than normal,
too, although he really hadn't focused
on them.
Watson mulled this over and then told
Annecchini that he could think of only one
possible explanation for what Annecchini
was seeing on his CGR-30P.
Prime suspect: the EDC
Watson knew that the CGR-30P uses
a remote-mounted module called the
Engine Data Converter (EDC) to take the
millivolt analog signals from the thermocouple
temperature sensors and convert
them to digital temperatures that are then
sent via a serial datalink to the panelmounted
CGR-30P display.
Watson was confident the reason the
CGR-30P was lying about all those temperatures
had to be an analog problem and
therefore something related to the EDC.
Although it could have been an internal
EDC failure, Watson suspected that a
bad (high-resistance) ground connection
between the EDC and the airframe was
the most likely explanation.
Watson asked Annecchini if he could
locate the EDC, explaining that it was a
small 4-by-6-inch metal box that is usually
mounted somewhere on the cockpit side of
the firewall and has several thick bundles
of wires connected to it.
Annecchini stuck his head under the
instrument panel and looked around. " I'm
pretty sure I found it! " he told Watson.
" Try wiggling the plugs that connect
The CGR-30P uses a remote-mounted EDC module to convert analog sensor data to digital data that it sends to the cockpit display.
AOPA PILOT / January 2025
87

AOPA Pilot Magazine - January 2025

Table of Contents for the Digital Edition of AOPA Pilot Magazine - January 2025