Citationjet (C525/C526) - CJ I / II / III / IV
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Flight Crew Last 90 Days 62; Flight Crew Total 3468; Flight Crew Type 312
Workload; Troubleshooting
Aircraft Equipment Problem Critical
Aircraft Equipment Problem Dissipated; Flight Crew Overcame Equipment Problem
Human Factors; Aircraft
Upon starting descent from FL390 the amber boxed autopilot out of trim box appeared on both PFD's. After reviewing the abnormal checklist; the captain disconnected the autopilot and the aircraft made an uncommanded pitch up; which was arrested with manual control wheel pressure. Next; in the course of running the abnormal checklist the Captain discovered the pitch trim wheel was frozen and unable to be moved up or down with manual or electric trim. The Captain was able to maintain positive control of the aircraft using heavy forward pressure on the control wheel except for the brief moment when the autopilot was disconnected and we did not deviate from ATC instructions. Therefore; an emergency was not declared at the time.Upon reaching warmer air; around 11;000 MSL; the pitch trim freed up. A normal descent and landing at our destination airport followed.
CE-525 First Officer reported the pitch trim wheel was frozen at the top of descent.