An improper traffic pattern entry was made by a PC12 Test Pilot returning from a test flight on which an uncommanded input moved the rudder full right and the system did not respond to subsequent manual override attempts.

Narrative

A flight supporting return to service of a PC12 was conducted. Flight was conducted with the dual purpose of validating airplane operation after a two-year hiatus (FCF) and defining the requirement for stall characteristics flight-testing with the upgraded PT6A-67P engine installed and operating at rated power (14 CFR 23.201/.203). Coming off the fifth stall I noted that the rudder trim had been driven to the right hand stop. After stabilizing in level flight at 160 KIAS we attempted; without success; to center the trim manually as the auto trim system was not responding. We returned to base at 120 KIAS with both feet on the left pedal. Normal traffic is right traffic for Runway 30. Preoccupied with the situation at hand; we told the Tower we'd enter left traffic for Runway 30 while entering the usual right traffic for Runway 30. On downwind the Tower commented 'oh you meant your other left.' The landing was uneventful. Neither the right seat pilot nor the Flight Test Engineer (FTE) caught the error until the Tower commented when we called downwind.