MD80 crew had autoplt give an uncommanded turn and an uncommanded descent.

Attributes
ACN	422186
Time
Date	199812
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : irk
State Reference	MO
Altitude	msl bound lower : 32500 msl bound upper : 33000
Environment
Light	Night
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Operating Under FAR Part	Part 121
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
ASRS Report	422186
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial
ASRS Report	422320
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude non adherence : far other anomaly other
Independent Detector	other flight crewa
Resolutory Action	other
Consequence	Other
Supplementary
Air Traffic Incident	other

Narrative:

Altitude deviation. FL330, 33 NM northwest of irk, on top, autoplt on. Cleared to turn left. The aircraft rolled left to heading, then engine EPR's split. Aircraft rolled 30 degree bank and descended. Captain recovered and turned on engine heat. Aircraft descended to FL325 during this maneuver. We assume engine icing on the left engine caused this event. We were in clear on top at FL330. No traffic conflict.

Original NASA ASRS Text

Title: MD80 CREW HAD AUTOPLT GIVE AN UNCOMMANDED TURN AND AN UNCOMMANDED DSCNT.

Narrative: ALTDEV. FL330, 33 NM NW OF IRK, ON TOP, AUTOPLT ON. CLRED TO TURN L. THE ACFT ROLLED L TO HDG, THEN ENG EPR'S SPLIT. ACFT ROLLED 30 DEG BANK AND DSNDED. CAPT RECOVERED AND TURNED ON ENG HEAT. ACFT DSNDED TO FL325 DURING THIS MANEUVER. WE ASSUME ENG ICING ON THE L ENG CAUSED THIS EVENT. WE WERE IN CLR ON TOP AT FL330. NO TFC CONFLICT.

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.