Double Trim Runaway

[pelmet]

From TSB....

C-GKAO, a Pilatus PC-12/47E operated by Keewatin Air LP (dba Kivalliq Air), was conducting
flight KEW404 from Morden Regional Aerodrome (CJA3), MB, to Winnipeg/James Armstrong
Richardson International Airport (CYWG), MB. After departing and at approximately 5000 feet, the
flight crew engaged the autopilot. The autopilot engaged, then disengaged, and "autopilot fail" and
"yaw damper fail" messages were illuminated. The flight crew determined the aircraft was in a
slipping attitude and ascertained that the rudder trim was fully deflected to the left and the aileron
trim was fully deflected to the right. Control of the aircraft was maintained through physical strength
on the flight controls and the aircraft was retrimmed. The flight crew engaged the autopilot again
and the rudder trim deflected to the left again. The crew immediately disconnected the autopilot,
retrimmed the aircraft and continued by hand-flying the aircraft. The flight crew referred to the quick
reference handbook and found there was no published procedure to address this failure. The flight
continued under visual meteorological conditions at a reduced airspeed and landed safely in
CYWG.
The aircraft was removed from service and the operator replaced the trim adapter unit.

[Dry Guy]

Great job by Pilatus not allowing an extreme trim position that can't be overpowered.

[digits_]

Great job by Pilatus not allowing an extreme trim position that can't be overpowered.

Seems more like a shitty job that one failed component can lead to a double trim runaway? Kudos though that they failed in opposite directions. Was that pure luck or by design?

[Eric Janson]

Not familiar with the PC-12.

Sounds like a rudder trim issue with the autopilot trying to compensate with aileron until the limits were reached.