EI’s US- 8 Ultimate Scanner displays absolute digital EGT information, as does
JPI’s EDM-700, and subsequent generations of digital engine monitors have
all done the same.
Things started getting confusing when Electronics International
(EI) introduced its Ultimate Scanner that provided digital (rather
than graphical) readouts of EGT, and touted its 1-degree Fahrenheit
accuracy as being far superior to the 25-degree granularity of the
GEM’s bar graph. (Never mind that the absolute EGT values it was
reporting so accurately were essentially meaningless.) Not to be
outdone, J.P. Instruments (JPI) introduced its EDM-700 that featured both a GEM-like bar graph and an Ultimate Scanner-like
digital readout on the same instrument (See Figure 2). The EDM-
700 was a smashing market success and forced both EI and
Insight to respond with similar products (the UBG- 16 and GEM
610, respectively).
Now pilots were being presented with precise digital values of
absolute EGT, scary temperatures in the 1,300s, 1,400s, 1,500s, and
even 1,600s Fahrenheit. Few understood what these temperatures
meant, but most assumed that—as with most other temperatures in
aviation (cylinder head temperature, turbine intake temperature,
outside air temperature, oil temperature, etc.)—cooler was better
and hotter was worse.
WHAT EGT IS NOT
In fact, however, absolute values of EGT are not particularly inter-
esting for a number of reasons. The most important is that indicated
EGT is not a “real” temperature. To understand what I mean by this,
