AOPA Pilot Magazine - December 2022 - 85

AVIONICS /
'Trust your instruments'
The Garmin GI 275 passes an extreme test
BY DAVE HIRSCHMAN
" TRUST YOUR INSTRUMENTS " is a timehonored
IFR flying maxim-but how
trustworthy are your instruments?
Pilots have no choice but to rely on the
gauges if we want to stay right-side up in
the clouds and find our destinations in low
visibility. But we also know the vacuum systems
that have traditionally powered our
attitude instruments are failure prone-and
the mechanical instruments themselves
have limitations that make them unreliable
in extreme pitch and roll excursions.
That's why we've come up with elaborate
instrument cross-checks and put so much
emphasis on partial-panel training.
Now, a new generation of digital, allin-one
attitude instruments has arrived
that promises to truly be worthy of
pilots' trust. The AOPA Extra 300L (see
" Teachable Moments, " p. 64) recently had
its electro-mechanical gyros replaced by
digital Garmin GI 275s at Southeast Aero,
and the results are much deeper than the
colorful synthetic vision image.
To put these new all-in-one attitude
instruments to a strenuous, real-world
test, we papered over the airplane's front
canopy so that the front-seat pilot (me) had
no view of the outside world at all. Then
Richard McSpadden, head of the AOPA Air
Safety Institute, put the Extra in a series of
progressively more extreme upsets while
flying in the unobstructed rear seat.
" Close your eyes and I'm going to
put the airplane in an unusual attitude, "
McSpadden said. Then, a moment later,
" Your airplane. "
Truthfully, I didn't close my eyes
because I was already in a cave of my own
making. But the recoveries from noselow
and nose-high attitudes with bank
angles of 90 degrees or so were remarkably
straightforward.
The GI 275 even draws a picture with a
trail of bright red arrows pointing the way
to level flight. There's no real scan involved,
either, since airspeed, altitude, and heading
all are displayed on the same instrument.
Then McSpadden got more aggressive
with pitch attitudes approaching vertical
and bank angles in excess of 120 degrees.
Still, the GI 275 showed the way back to
level flight every time, and my only real
decision was whether to fix the pitch or
roll problem first. (Personally, in nosehigh
attitudes, I prefer to let the nose come
down to the horizon first and then correct
the bank angle.)
During our preflight briefing, we'd
decided that if the upset recoveries went
well, I'd attempt some basic aerobatic
maneuvers under the hood.
Aileron rolls in each direction were a
simple flick of the wrist, and the GI 275s
weren't bothered by the Extra's unusually
quick roll rate.
Next, I tried a series of " over-the-top "
maneuvers-loops and half-Cuban eights.
They looked good on the GI 275, but
McSpadden said they were sloppy, with
headings straying as much as 20 degrees
by the end of each maneuver. The only
novel part of flying the figures was that
it required intentionally disregarding the
GI 275's recovery arrows, and those things
are so prominent and insistent that they
gave me a momentary pause before overruling
them.
The final under-the-hood maneuver
was an upright spin. At idle power, full aft
stick, and full left rudder, the Extra obediently
tucked into a spin and the GI 275
displayed a 70-degree nose-down pitch
attitude and rotation. Opposite rudder and
forward stick stopped the rotation after
about three turns, and I held the Extra in
a nearly vertical dive for a few seconds as
airspeed increased, then initiated a normal
recovery.
The GI 275 isn't going to replace a
sighting device for competition aerobatic
pilots. Looking outside is still more immediate
and accurate than interpreting an
instrument. But the GI 275 stayed oriented
throughout 360 degrees of pitch and roll
and showed the way to level flight.
GI 275s are widely used as primary
and standby attitude indicators, and
some come with backup batteries that
keep them going without ship's power.
They rely on GPS for heading information,
so it's likely that sustained inverted
flight would block the GPS antenna from
reading the satellites that let it know
its position. But the instruments didn't
seem to mind having their satellite
reception compromised for a few seconds
at a time.
As Garmin's GI 275, less sophisticated
G5s, and other solid-state attitude instruments
made by other manufacturers get
more broadly installed throughout the
general aviation fleet, IFR flight training is
likely to change. Turn coordinators seem
totally obsolete, for example, and using
them (along with vertical speed indicators
and altimeters) to identify and recover
from upsets in the clouds seems to belong
to a bygone era.
That old truism about trusting your
instruments, however, is becoming truer
than ever. dave.hirschman@aopa.org
Garmin GI 275s, like the one in the center
of the panel in the AOPA Extra 300L
(opposite page), remain oriented during
aerobatic maneuvers, and they aren't
harmed by extreme pitch and roll attitudes
or abrupt maneuvering.
AOPA PILOT / December 2022
85
AOPA Pilot Magazine - December 2022

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