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Status	Accident investigation report completed and information captured
Date	Friday 28 April 1995
Time	12:00 LT
Type	Airbus A320-211
Operator	Northwest Airlines
Registration	N331NW
MSN	318
Year of manufature	1992
Engines	CFMI CFM56-5
Crew	Fatalities: 0 / Occupants:
Passengers	Fatalities: 0 / Occupants:
Total occupants	Fatalities: 0 / Occupants: 90
Aircraft damage	None
Location	Minneapolis, MN United States of America
Phase	En route
Nature	Unknown
Departure Airport	, MN (KMSP)
Destination Airport	Orange County, CA
Narrative	ON TWO CONSECUTIVE DAYS, THE SAME AIRPLANE EXPERIENCED UNCOMMANDED ROLLS DURING FLIGHT WITH THE AUTOPILOT ENGAGED. INSPECTION OF THE AIRPLANE SYSTEMS REVEALED A DEFECT IN A ROLL POTENTIOMETER LOCATED IN THE CAPTAINS SIDESTICK TRANSDUCER UNIT. A GREASE FILLED GROOVE WAS FOUND IN THE POTENTIOMETER TRACK NEAR THE NEUTRAL POSITION. THIS POTENTIOMETER SENDS ELECTRONIC SIGNALS TO THE ELEVATOR AILERON CONTROLLER (ELAC-1). THE GROOVE RESULTED IN AN INTERMITTENT LOSS OF CONTACT BETWEEN THE WIPER AND THE TRACK AND SUBSEQUENTLY A 'VOLTAGE SPIKE' TO THE ELAC-1. FOLLOWING THIS INCIDENT AIRBUS ISSUED TWO SERVICE BULLETINS ADDRESSING THE 'VOLTAGE SPIKE' PHENOMENON WHICH HAS BEEN OCCURRING ON OTHER A320 AIRPLANES SINCE 1991. Probable Cause: inadequate design of the fly-by-wire flight control system which allowed false signals from the sidestick transducer units to generate uncommanded rolls.

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