The incorrect entry of longitudinal information prior to an AirAsia X flight on the Sydney-Kuala Lumpur route caused serious issues with aircraft's systems after it became airborne.

Prior to the flight, the captain inadvertently entered inaccurate longitudinal information in the flight management and guidance system, says the Australian Transport Safety Bureau (ATSB) in a final report into the incident.

The error would have placed the aircraft, an Airbus A330-300 registered 9M-XXM, about 11,000km to the west, off the coast of Cape Town, South Africa.

Although the crew received some indications prior to take-off of system issues, they carried out the take-off as planned. Shortly after take-off from Sydney's runway 16R, however, air traffic control observed the jet enter the departure flightpath of a parallel runway, 16L.

"Following advice from air traffic control, the flightcrew identified a problem with the onboard navigation systems," it said. "Attempts to troubleshoot and rectify the problem resulted in further degradation of the navigation system, as well as to the aircraft's flight guidance and flight control systems."

The crew decided to return to Sydney, but poor weather and the aircraft's degraded systems limited the aircraft to visual conditions. The crew ended up flying to Melbourne manually. After a go-around at Melbourne airport caused by a spurious enhanced ground proximity warning system alert, they landed without further incident.

The entire flight took 1h 54 min, and after a few hours on the ground, and "extensive troubleshooting", no faults were found. After 3h, the aircraft departed for Kuala Lumpur without further incident.

"The aircraft was not fitted with an upgraded flight management system that would have prevented the data entry error via either automated initialisation or automatic correction of manual errors," says the ATSB.

Following the incident, the airline issued a bulletin stressing the importance of programming the correct data into to the air data and inertial reference system (ADIRS). It also reviewed recovery procedures with its flightcrews.

"This occurrence highlights that even experienced flightcrew are not immune from data entry errors," it adds.

"However, carrying out procedures and incorporating equipment upgrades recommended by aircraft manufacturers will assist in preventing or detecting such errors. Additionally, the airborne management of this occurrence illustrates the importance of effective communication when dealing with an abnormal situation under high-workload conditions. This is especially the case when there is limited guidance available to resolve the issue."

The pilot had 22,580h of flying experience, mainly in Boeing types, while the first officer had 2,200h. Including the flightcrew, there were 10 crew and 212 passengers aboard the jet.

Source: Cirium Dashboard