On 15 October 2008, the aircraft manufacturer issued Operations Engineering Bulletin (OEB) OEB-A330-74-1, which was applicable to all A330 aircraft fitted with Northrop Grumman ADIRUs. The OEB stated that, in the event of a NAV IR [1, 2 or 3] FAULT (or an ATT red flag being displayed on either the captain’s or first officer’s primary flight display), the flight crew were required to select the air data reference (ADR) part of the relevant ADIRU OFF and then select the relevant inertial reference (IR) part of the relevant ADIRU OFF. The problem was described as a ‘significant operational issue’ and operators were advised to inform their pilots of the OEB without delay and insert the procedure in the Flight Crew Operations Manual. A compatible temporary revision was issued to the Minimum Master Equipment List at the same time.
Note: Operators were advised of the OEB and the associated problem in an operator information telex that was issued on 14 October 2008.
The OEB procedure was subsequently amended in December 2008 to cater for a situation where the IR and ADR pushbuttons were selected OFF and the OFF lights did not illuminate. The new OEB (A330-74-3) required crews to select the IR mode rotary selector to the OFF position if the lights did not illuminate.
Following the 27 December 2008 occurrence, the aircraft manufacturer issued another OEB (A330-74-4, 4 January 2009). This OEB provided a revised procedure for responding to a similar ADIRU-related event to ensure incorrect data would not be used by other aircraft systems. The procedure required the crew to select the relevant IR OFF, select the relevant ADR OFF, and then turn the IR mode rotary selector to the OFF position.
The manufacturer issued similar OEBs to operators of A340 aircraft.
The ATSB is satisfied that related action being taken by the aircraft manufacturer to redesign the algorithm will satisfactorily address the safety issue.