NTSB Identification: CHI95IA342.
The docket is stored in the Docket Management System (DMS). Please contact Records Management Division
Scheduled 14 CFR (D.B.A. NORTHWEST AIRLINES )
Incident occurred Friday, April 28, 1995 in MINNEAPOLIS, MN
Probable Cause Approval Date: 04/29/1996
Aircraft: Airbus Industrie A320-211, registration: N331NW
Injuries: 90 Uninjured.

NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.

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.

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

inadequate design of the fly-by-wire flight control system which allowed false signals from the sidestick transducer units to generate uncommanded rolls.

Full narrative available

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