Ce-525 first officer reported the pitch trim wheel was frozen at the top of descent.

Attributes
ACN	1572548
Time
Date	201808
Local Time Of Day	1801-2400
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Make Model Name	Citationjet (C525/C526) - CJ I / II / III / IV
Operating Under FAR Part	Part 91
Flight Phase	Descent
Route In Use	Direct
Flight Plan	IFR
Component
Aircraft Component	Elevator Trim System
Person 1
Function	Enroute First Officer Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 62 Flight Crew Total 3468 Flight Crew Type 312
Events
Anomaly	Aircraft Equipment Problem Critical

Narrative:

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.

Original NASA ASRS Text

Title: CE-525 First Officer reported the pitch trim wheel was frozen at the top of descent.

Narrative: 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.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.