Description

On 11 January 2007, an Air New Zealand Airbus A320 which had just departed Sydney Australia for Auckland, New Zealand on the first flight of the day was observed to have turned onto a heading contrary to the ATC-issued radar heading. When so advised by ATC, the crew checked the aircraft compasses and found that they were reading approximately 40 degrees off the correct heading and that a ‘GPS PRIMARY LOST’ message had appeared on the MFD and the NDs.

“The crew then advised ATC that they had navigational difficulties and elected to return to Sydney for landing. When the aircraft returned to the departure gate, the flight crew noticed that the inertial reference system (IRS) had been aligned to the incorrect longitude. The operator subsequently found that the IRS had been aligned by maintenance staff prior to the crew boarding the aircraft. The incorrect alignment of the IRS was not detected during a number of subsequent checks prior to departure".

The ATSB Investigation Report was published in April 2008 and found that: