Sam aircraft has runaway electrical trim. Altitude deviation.

Attributes
ACN	181864
Time
Date	199106
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : jot
State Reference	IL
Altitude	msl bound lower : 3000 msl bound upper : 5000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ord
Operator	general aviation : corporate
Make Model Name	Small Aircraft, Low Wing, 1 Eng, Retractable Gear
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : commercial pilot : instrument
Experience	flight time last 90 days : 15 flight time total : 400 flight time type : 15
ASRS Report	181864
Person 2
Affiliation	government : faa
Function	controller : departure
Qualification	controller : radar
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude
Independent Detector	other other : unspecified cockpit
Resolutory Action	flight crew : overcame equipment problem flight crew : returned to intended course or assigned course
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation other

Narrative:

At cruise flight with the autoplt engaged the aircraft's electric trim rotated forward on its own resulting in a fairly steep descent. Realizing the autoplt was malfunctioning, I tried to turn it off. I pushed the electric trim button, then the red disconnect button and then tried to turn off the autoplt at the panel. The autoplt could not disengage and the trim continued to run. It was only after I pulled the autoplt's cbs that the system would disengage. As a result, I lost 2000' in altitude.

Original NASA ASRS Text

Title: SAM ACFT HAS RUNAWAY ELECTRICAL TRIM. ALT DEVIATION.

Narrative: AT CRUISE FLT WITH THE AUTOPLT ENGAGED THE ACFT'S ELECTRIC TRIM ROTATED FORWARD ON ITS OWN RESULTING IN A FAIRLY STEEP DSNT. REALIZING THE AUTOPLT WAS MALFUNCTIONING, I TRIED TO TURN IT OFF. I PUSHED THE ELECTRIC TRIM BUTTON, THEN THE RED DISCONNECT BUTTON AND THEN TRIED TO TURN OFF THE AUTOPLT AT THE PANEL. THE AUTOPLT COULD NOT DISENGAGE AND THE TRIM CONTINUED TO RUN. IT WAS ONLY AFTER I PULLED THE AUTOPLT'S CBS THAT THE SYS WOULD DISENGAGE. AS A RESULT, I LOST 2000' IN ALT.

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.