"Bart" wrote in message
...
Not true in many (most) turbines.

wrote:
On most helicopters that I have been in, testing the split (sprag
clutch) is part of the power on preflight. It seems kind of odd that
such a catastophic clutch failure would occur without warning in the
preflight. Perhaps they skipped that step.

I remember part of the Bell Jetranger preflight was to turn the blades by
hand to 90/270, and you were supposed to turn them counter clockwise (the
direction of normal rotation), I can't remember the reason why that
particular direction was specified. Maybe so as to not spin the power
turbine (and engine RGB) without proper lubrication, maybe it was to check
for sprag clutch disengagement, maybe both reasons.

As for testing the _engagement_ of the clutch on preflight, my first thought
is that it is impractical. Even on a small ship like the Scorpion, the main
rotor may normally experience several hundred pounds-feet of torque...

For another data point, I can say that checking the freewheeling unit(s) is
not a part of the H-60 preflight, the navalized version anyway.

On a related anecdote, when one of my friends was a student pilot, he had a
hard landing when the sprag clutch failed to reengage following a practice
power recovery autorotation. It freewheeled just fine though, and it
engaged fine up until before the auto. That is the only time I ever heard
of such a thing happening.