BA2014-093-4P-1:

The Investigating Committee of TSB of Hungary concluded during the investigation that the causes of the right aileron fault which then caused the incident were as follows:
- previous to the examined flight, the right aileron blue servocontrol was deactivated according to Section 27-14-04A of the MEL.
- The ELAC1 computer, which was responsible for the operation of the ailerons, malfunctioned during the flight.

Depending on the type of operation, the airplanes in the Airbus A320 family perform 6 to 8 flights per day on average (i.e. 60 to 80 flights within a 10-day interval), and, according to relevant sections of the MEL, the operability of only one servocontrol is required on any or both of the ailerons. (The left aileron green servocontrol (according to MMEL 27-14-02) and the right aileron blue servocontrol (according to MMEL 27-14-04) may be inoperative concurrently for an interval of 10 days.)

The Transportation Safety Bureau of Hungary recommends Airbus Industrie to revise and, if possible reduce, the 10-day interval relevant to unserviceable aileron servocontrols listed in pages MMEL27-14-01 to MMEL27-14-04 in the Airbus A318/A319/A320/A321 Master Minimum Equipment List document.

The Investigating Committee considers that in the case of accepting and implementing the above recommendation, the number of those flights within the Airbus A320 family of aircraft may be reduced significantly where the fly-by-wire type Flight Control system operates in single-channel mode. This would reduce the risk of an aileron fault caused by a computer (ELAC1 or ELAC2) fault alone.