I have a question about a propeller and engine overspeed in the TSIO 550.
Recently there was such an event where apparently the governor failed and
allowed the prop to go to around 3300 RPM.  The experimental aircraft
referenced had about 20 hours of phase I flight with no particular engine
issues to date other than fine tuning fuel flows and such.  The engine was a
new factory built Continental but had been purchased several years ago.  I
think the accessories including the governor were likely new parts as well.

The test pilot reported that the overspeed lasted about 15 seconds and until
that time did not respond to the blue knob OR to throttle.  Even when the
engine was brought back to idle (possibly it was only retarded to 14" MAP)
the propeller RPM did not respond.  Finally after the time frame mentioned
the prop became responsive to input and the pilot achieved an on airport
landing with no further damage.

Disassembly revealed that the prop governor shaft would turn in one
direction only so the presumptive diagnosis is that the governor seized up
causing the overspeed.  Further examination, tear down and tests will
hopefully shed more light, but my question is how could the RPM remain at
3300 when the throttle is brought back to idle, if indeed the MAP dropped to
an idle or near idle condition.

Thanks for your opinions.


Regards,

John Barrett, CEO
Leading Edge Composites
PO Box 428
Port Hadlock, WA 98339
www.carbinge.com