A captain’s data-entry error when programming an AirAsia X Airbus A330-300’s initial coordinates, which led to myriad navigation errors and an eventual diversion, would have been caught if an Airbus-recommended upgrade had been installed. But despite recurring problems with the old systems, the upgrade was not mandatory, Australian investigators found.
The March 10, 2015, incident began when the captain entered incorrect coordinates into the A330’s air data and inertial reference system (ADIRS). The longitude was incorrectly entered as 01519.8 east (15 deg. 19.8 min. E. Long.) instead of 15109.8 east (151 deg. 9.8 min. E. Long.). As a result, the aircraft’s systems placed it near Cape Town, South Africa, instead of at Sydney Airport’s International Terminal Gate 54.
“The magnitude of this error adversely affected the aircraft’s navigation functions, global positioning system (GPS) receivers and some electronic centralized aircraft monitoring alerts,” the Australian Transport Safety Bureau (ATSB) report on the incident states. “[D]espite a number of opportunities to identify and correct the error, it was not noticed until after the aircraft became airborne and started tracking in the wrong direction.”
The flight crew did not realize it had a problem until a series of warnings upon takeoff en route to Kuala Lumpur. The crew then attempted to follow the course assigned by air traffic control, including a right turn. But the aircraft, operating on autopilot and guided by the erroneous starting coordinates, turned left instead, crossing the departure path of a parallel runway.
After nearly an hour of fruitless troubleshooting, the crew diverted to Melbourne Airport; weather at Sydney had deteriorated, and the AirAsia X crew, suspecting navigation problems, wanted a visual approach.
The incident’s cause was clear: The mistyped longitude triggered a series of events that led the flight crew to believe the aircraft had malfunctioning avionics. But extensive postincident troubleshooting concluded that the only problems were human factor-related: erroneous data entry and missed clues that would have highlighted the problem.
But the ATSB also highlighted a service bulletin (SB) detailing an ADIRS upgrade that became available in 2013 for the A330 and other Airbus models. The upgrade allows position initialization to occur automatically using GPS, or, “in the event the initialization is carried out manually, when the pilot-entered initialization position is crosschecked with the GPS position.”
The ATSB says about 515 aircraft were eligible for the SB upgrade, but only about half had undergone the work. AirAsia X, “for reasons that could not be determined,” was among the operators that upgraded their aircraft, it says.
“Airbus records suggest that approximately two occurrences are reported per annum that are attributable to position initialization error in aircraft that have not been upgraded,” the ATSB says.