AOPA Turbine Pilot Magazine - January 2025 - 83

range. In a strong headwind,
for example, a
faster-than-best-glide
airspeed will reduce
the amount of time the
airplane is subjected
to a headwind and
reduce the resulting
loss of glide distance.
Similarly, with a tailwind,
pilots should fly
a slower indicated airspeed
than best glide to
maximize the duration
of nature's push and
increase gliding distance.
Garmin air data
computers know and
constantly update wind
strength and direction-
yet the company doesn't
use that information to
adjust the manufacturer-supplied bestglide
speed for current conditions.
Dynon
Dynon added an " Emergency Glide " feature
SkyView HDX update on August 20, 2024,
that engages the autopilot to fly directly to
the nearest suitable airport at best-glide
speed. It shows a green glide-range ring on
the moving map. The Dynon glide ring is
circular at all times and its shape changes
to account for mountainous terrain-but
Emergency Glide takes terrain elevation
into account when selecting target airports.
I made a series of flights in my Dynon
SkyView-equipped Van's Aircraft RV-4
and set up each glide in the same way:
an altitude of 4,000 feet or above, airport
barely within the graphical glide ring.
Then I'd engage Emergency Glide (by
holding down the NRST button for two
seconds or more) and let the airplane turn
directly to the airport at idle power and the
prop in its full high-pitch/low-rpm setting.
Dynon requires pilots of airplanes
registered in the experimental/amateurbuilt
category (such as the RV-4) to set
their airplane's glide ratio and rate of
descent because each aircraft is likely to
vary, and sometimes they vary widely.
Van's Aircraft doesn't provide glide
ratios, so I turned to pilots and builders
of similar airplanes who provided
must pick an off-airport
landing site.
There's no reason
Dynon's Emergency Glide draws a green circle with the aircraft in the center to show glide
range, and that circle accounts for wind but not terrain. Here, the airplane is flying at 7,000
feet, about five miles from Palm Springs International Airport (PSP), and the green circle
shows the airport is within glide range.
guestimates of about 9:1. My airplane's
real-world, idle-power performance was
closer to 8:1 with a 950-foot-per-minute
rate of descent. Those stubby, low-aspectratio
wings just aren't efficient gliders.
One glide-ring characteristic that
became clear during the Dynon/RV-4
glide flights was that headwinds at cruise
altitude are far more likely to result in successfully
reaching airports than tailwinds.
That seems counterintuitive but headwinds
are almost certain to diminish as a gliding
airplane descends to lower altitude-and
that reduced headwind increases glide
range. Similarly, a tailwind at cruise altitude
is also likely to diminish during a descent.
That decreasing push leads the glide rings
to rapidly constrict-and that makes it less
likely a gliding airplane will reach its target.
During headwinds or tailwinds of 10 knots
or more, my airplane's glide performance
was noticeably better when I adjusted the
best-glide speed while hand flying instead
of using autopilot.
Conclusions
The main benefit of glide rings is that
they constantly give pilots this bit of
unsettling news: We're seldom within
gliding distance to an airport, even at
normal cruise altitudes above populated
regions. In a real engine-out emergency,
glide rings show pilots instantly that they
to waste precious time
with distractions such as
searching for and choosing
a nearby airport,
turning in its direction,
changing radio
frequencies, and estimating
whether or not you'll
be able to glide there. You
won't, don't bother trying.
The trickiest aspect
of glide rings is that they
give the appearance
of omniscience when
they're really just living
in the moment. They
make constant calculations
and update the pilot
every three seconds-yet
they don't predict how much the wind is
going to shift in speed or direction at lower
altitudes, and they don't show the pilot
the optimal speed to fly to maximize glide
range based on current conditions.
For pilots who begin a glide to an airport
that appears within glide range only to
see it slip away as the rings constrict during
descent, the sense of betrayal is severe.
After all, as an airplane flies in the direction
of a suddenly out-of-reach airport, it's
likely heading toward a more developed
area with fewer suitable off-field landing
sites. Pilots can find out for themselves
by practicing power-off glides in various
wind conditions to determine whether
their anticipated glide range is accurate.
Pilots also can improve glide performance
by moving constant-speed propellers to
the high pitch/low rpm setting; pitching
up momentarily to stop props from adding
drag by windmilling; flying faster than the
published best-glide speed in a headwind
and slower with a tailwind.
Glide rings provide a great deal of
potentially life-saving information at a
glance. When linked to an autopilot, they
reduce pilot workload and avoid potential
losses of aircraft control at critical
moments. Like other safety tools, however,
understanding what goes into them
is the key to getting the most out of them.
dave.hirschman@aopa.org
AOPA PILOT / January 2025
83

AOPA Turbine Pilot Magazine - January 2025

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