Maintenance personnel failed to reconnect a rudder trim control rod on an Air Tahiti ATR 72-200 before the aircraft departed, prompting the crew to return to the airport, an inquiry has found.
As the aircraft climbed away from Papeete, French Polynesia at about 170kt (315km/h), the captain discovered the balance ball of the turn indicator was deflected fully to the right.
Efforts to rebalance the aircraft only managed to bring the ball to a position midway between the centre and the right-hand stop.
Having determined the instrument was not faulty, and concerned he would be unable to trim the turboprop in the event of a left-hand engine failure, the captain opted to abort the flight. Maintenance conducted after the incident revealed the rudder trim control rod was disconnected.
French investigation authority BEA says the ATR 72 had undergone a three-week maintenance visit concluding on 24 June 2011, the day before the incident, when inspection of the rudder torque tube revealed corrosion. A technician assigned to treat the problem disconnected the rudder trim control rod but limitations in the maintenance computer system meant only the beginning and end of the procedure - and not each individual step - could be recorded.
As a result, disconnection of the control rod was omitted from the record. When a separate mechanic completed the task, the rod was not reconnected. BEA adds that because no work was originally planned on the rudder component, it went unchecked and untested by supervisors. Control-surface deflection checks were also insufficient.
BEA says the "incomplete implementation and verification" of the maintenance operation, to which the computer system limitations contributed, resulted in the oversight.
Air Tahiti subsequently proposed several measures to prevent a recurrence, says BEA, including improved task tracking on work cards to back up computer records.