Pilot reports of uncommanded rolls between 5¹ and 30¹ in Airbus A320s and A321s have led to a US Federal Aviation Administration proposed airworthiness directive (PAD) for fleet-wide modifications to the elevator and aileron computers (ELACs).
Airbus, however, says that 90% of the world fleet and all US-registered aircraft have been modified in advance of the PAD following an August 1995 service bulletin from the manufacturer. The company claims that uncommanded rolls had been limited to 5¹, explaining that aileron over-sensitivity in specific situations had led pilots to over-control in roll. Modifications, says Airbus, consisted of changes to the ELACs' software, which reduced aileron sensitivity.
The French Direction Générale de l'Aviation Civile had notified the FAA that the vulnerable situations were associated with flap settings 3 or full, in which overcontrolling could happen too easily. Also, when a system designed to prevent asymmetric-flap deployment immobilised the flaps, with the flap lever at 3, "roll oscillations" could occur. Airbus says that associated messages on the electronic central aircraft-monitor display have also been clarified.
Finally, the PAD says contaminants in the sidestick's transducer have caused the ailerons to "jerk". Airbus says that this was traced to electrical "spikes" produced by the control's potentiometer.
Source: Flight International
