"Michael 182" wrote in message
newsw24d.81563$MQ5.65618@attbi_s52...
Glad the chute worked, but what would cause an airplane to stall at 16,000
feet, then encounter turbulence that would send it into a spin at 15,000
feet? At that height it would seem a stall should be pretty simple to
recover from, although, once again, I can't imagine what would make the
plane stall in the first place during cruise.


The airplane was near the service ceiling and may already have been at a
high angle of attack. Flying slowly because of the turbulence may have
increased the angle of attack still further. If the turbulence is severe the
airplane could exceed the critical angle of attack. Picture the airplane in
a straight and level attitude but descending straight down and you get the
idea -- very high angle of attack. This would especially be true if the
airplane was in a rapid descent because of the turbulence and the pilot was
trying to maintain altitude or even a straight and level attitude. If the
airplane is uncoordinated then the stall could turn into a spin. Picture
again the airplane moving straight down in a level attitude, but now one
wing is moving backward relative to the other. That wing will have a higher
angle of attack than the other; it will stall without warning and the
airplane will immediately begin to roll into a spin, possibly even inverted.
Of course, the turbulence would have to be pretty bad to cause this, but in
the Central Valley in the vicinity of thunderstorms, I can believe it. The
stall resistant Cirrus might hold out longer than other airplanes, but it is
not invulnerable.

Cirrus deliberately limited rudder and elevator travel to prevent stalls and
spins. This has the effect, however, of making it more difficult or even
impossible to recover once a spin develops. There is not enough rudder
authority to recover. The Cirrus has never demonstrated a spin recovery,
though it has been tried. The only way the airplane could receive
certification was to require deployment of the parachute in the event of a
spin.

There seems to be a pattern of Cirrus aircraft entering stalls and spins in
turbulence at high altitudes. It may be a training problem -- pilots taking
Cirrus airplanes into conditions that they would not try in other airplanes.
For now, I think that if you take a Cirrus into turbulence at high altitude
there is a certain risk that the airplane will be lost. That risk may be
more or less than other types, but it is there.