Incident Overview
On two consecutive days, the same airplane experienced uncommanded rolls during flight with the autopilot engaged. The aircraft involved was an A320, as referenced in subsequent service bulletins. No other specific details about the operator, location, or date were provided.
Inspection Findings
Inspection of the airplane systems revealed a defect in a roll potentiometer located in the captain's 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, which subsequently produced a voltage spike to the ELAC-1.
Manufacturer Response
Following this incident, Airbus issued two service bulletins addressing the voltage spike phenomenon. The bulletins noted that similar occurrences had been observed on other A320 airplanes since 1991. No further details on the content of the service bulletins were provided.
Technical Context
The roll potentiometer is a component within the sidestick transducer unit that converts mechanical input from the captain's sidestick into electronic signals for the flight control computers. The grease-filled groove caused abnormal resistance changes, leading to the uncommanded roll events. The voltage spike to the ELAC-1, which processes aileron and elevator commands, likely triggered the autopilot disengagement or incorrect roll response.