AOPA Turbine Pilot Magazine - November 2021 - 78

It's a trip many general aviation
pilots dream of: flying general aviation
coast-to-coast, and these
pilots planned to do it almost literally
sea to shining sea. The
Bonanza G36 is one of the best
airplanes around for such a
trip. Sturdy, spacious, luxurious
seating, a Garmin G1000 for navigation,
and an IO-550 with 300
horsepower to pull them along at
175 KTAS. It's an exciting adventure.
The gap in their planning
was that both pilots were flatlanders.
The gap would prove fatal
over the high terrain in Colorado.
The owner was based out of
New York, where terrain tops out
at 3,000 feet. The pilots probably
took comfort in the 300-horsepower
engine to get them up
and over the Rocky Mountains
at some four times that altitude.
They picked the airplane up in
California and flew to Aspen,
Colorado, uneventfully. The performance
in California was likely
what they were used to " feeling "
in New York: strong engine output
producing climbs at greater than
1,000 fpm, and responsive flight
controls.
Around 2 p.m. they landed
in Aspen (ASE) where altitudes
became a significant factor.
Colorado has the highest average
elevation of any state and the
highest average airport elevation.
Every year, the state is among the
top in the nation in density altitude
related aviation accidents.
The pilots lunched, fueled, and
waited. Perhaps the long delay
78
AOPA PILOT / November 2021
included time to wait for cooler
temperatures and more favorable
density altitude, but the temperature
at 6 p.m. was still 25 degrees
Celsius, 77 degrees Fahrenheit,
and density altitude was near
10,000 feet. After realizing they
couldn't accept the 16,000-foot
clearance (the minimum en route
altitude) on the LINZ 9 departure,
they decided to fly VFR and climb
while circling over Aspen until
they could make the crossing of
the imposing Sawatch Range to
the east, with peaks topping 14,000
feet. They flew several ascending
circuits, then at around 10,000
feet msl assessed that they had
enough distance to climb en route
and clear the more than 13,000foot
ridge to the east. A critical
misjudgment.
It's difficult to comprehend
the impact of density altitude on
aircraft performance. It's also
difficult to understand how fast
benign-looking terrain is rising.
Pilots focus on the big ridges
ahead, but it's seldom those that
kill. It's the gradually rising valley
floor that squeezes pilots between
a paltry maximum-performance
climb and deceptively rising terrain.
Focusing on the high ridges
in front, pilots often wait too long
to make the turn back. The floor
has risen, taking away any vertical
turning room. The canyon has narrowed,
limiting horizontal turning
room. At high density altitudes,
ground speed is greater, making
for a larger turn radius. Pilots
need more room for a 180-degree
turn than they are used to at sea
level. Exacerbating the problem,
airspeed bleeds off faster when
a pilot uses normal control pressures
to roll into a turn at high
density altitudes. Finally, there are
almost always up- or downdrafts
to contend with in the mountains.
In this case, the winds were from
the east at approximately 15 knots.
Approaching the ridge from the
west, the lee side, the pilots would
likely have been dealing with a
slight downdraft, slight enough
that they may not have identified
it, but they may have been alarmed
by the aircraft's eroding climb
performance.
As the pilots continued east,
terrain below rising, imposing
terrain ahead getting closer, and
aircraft performance decreasing,
they made a late decision to
abort the route and turn around
to escape back down the canyon.
But it was too late. From here it's
conjecture, but the cockpit was
steadily increasing in stress and
anxiety. At the decision point, the
friends knew they were in trouble.
They would have been on full
alert, perhaps suppressing panic.
Smooth, delicate control inputs
are essential when turning at high
density altitude. The turn would
seem to be grinding, plodding,
with a turn rate so slow, the side of
the canyon drawing nearer, and no
vertical room to use below them. It
takes a good cross check and good
discipline to avoid the sub-conscious
tendency to push bottom
rudder and pull the nose around
AOPA Turbine Pilot Magazine - November 2021

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