An light transport cpr crew had a trim problem causing an altitude deviation.

Attributes
ACN	224042
Time
Date	199210
Day	Tue
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : elm
State Reference	NY
Altitude	msl bound lower : 22000 msl bound upper : 22500
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zny
Operator	general aviation : corporate
Make Model Name	Light Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : commercial pilot : cfi pilot : atp
Experience	flight time last 90 days : 90 flight time total : 15000 flight time type : 3000
ASRS Report	224042
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : overcame equipment problem flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation other

Narrative:

Copilot was flying from the left seat. Center cleared us to a lower altitude. Copilot turned off the altitude hold on the autoplt to begin the descent and we experienced a runaway elevator trim to a nose-up position. Aircraft gained several hundred ft before I took control and got the aircraft going down -- no traffic conflict that I know about -- no comment from center. On the previous takeoff we had received a momentary autoplt out of trim annunciator. Aircraft is now in the radio shop.

Original NASA ASRS Text

Title: AN LTT CPR CREW HAD A TRIM PROBLEM CAUSING AN ALTDEV.

Narrative: COPLT WAS FLYING FROM THE L SEAT. CTR CLRED US TO A LOWER ALT. COPLT TURNED OFF THE ALT HOLD ON THE AUTOPLT TO BEGIN THE DSCNT AND WE EXPERIENCED A RUNAWAY ELEVATOR TRIM TO A NOSE-UP POS. ACFT GAINED SEVERAL HUNDRED FT BEFORE I TOOK CTL AND GOT THE ACFT GOING DOWN -- NO TFC CONFLICT THAT I KNOW ABOUT -- NO COMMENT FROM CTR. ON THE PREVIOUS TKOF WE HAD RECEIVED A MOMENTARY AUTOPLT OUT OF TRIM ANNUNCIATOR. ACFT IS NOW IN THE RADIO SHOP.

Data retrieved from NASA's ASRS site as of July 2007 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.