Pilots of an AirAsia X Airbus A330-300 bound for Kuala Lumpur lost almost all navigational information shortly after takeoff from Sydney due to an incorrect entry into the aircraft’s flight management and guidance system, an Australian Transport Safety Bureau (ATSB) investigation has found.
The ATSB report on the March 10 2015 incident, published on Wednesday, said the captain of the AirAsia X flight wrongly entered the longitudinal position of the aircraft into the A330’s flight management and guidance system (FMGS), resulting in errors in the alignment and initialisation of the aircraft’s air data and inertial reference system.
That mistake led to the Airbus, 9M-XXM, turning left after takeoff from Sydney’s Runway 16R instead of right. As a result, the aircraft, carrying 212 passengers and 10 crew, crossed the departure flightpath of the adjacent parallel Runway 16L.
The ATSB report said the error was not spotted by the first officer when cross checking the flight management and guidance system entries. The report said the first officer had seen a “flag or indication flash up on the captain’s navigation display (ND), but that it was too quick to interpret” and he had not mentioned it to the captain because there was no “associated electronic centralised aircraft monitoring (ECAM) or STATUS message.
“It is likely that data integrity checks detailed in the pre-flight and taxi checklists were either omitted or conducted with the navigation display selected to an inappropriate mode and/or range that concealed the aircraft’s positional error,” the ATSB report said.
“The instrument panels cockpit check was not carried out in accordance with the flightcrew operations manual and resulted in the crew not detecting the offset error in the displayed heading.”
The pilots also ignored a “single chime” or alert shortly after pushback from the gate that was usually an indication that the aircraft systems had detected a fault.
“Both flightcrew stated that they did not look towards the overhead panel or MCDU and, as there was no associated ECAM or STATUS message, they continued with normal procedures,” the ATSB said.
There were two more chimes while waiting to takeoff. However, the ATSB said the pilots decided to continue with the line-up to takeoff after checking the STATUS page and ECAM and finding “no other abnormal indications”.
Further, the aircraft was not fitted with an upgraded flight management system that would have corrected such kinds of data entry errors.
Indications something was not right continued after takeoff, when the aircraft’s enhanced ground proximity system (EGPWS) activated with the aural alert “terrain, terrain”.
As it was a day flight and the pilots could visually determine no terrain conflict existed, the captain instructed the first officer, who was the pilot flying, to ignore the warning and continue with the normal takeoff.
“Flight data of the occurrence flight identified that the autopilot was engaged at an altitude of 410ft and that the aircraft then commenced a gradual left turn over 14 seconds onto a magnetic heading of 132 degrees, although 170 degrees was being incorrectly displayed on the aircraft’s main heading indicators,” the ATSB said.
The ATSB said air traffic control was forced to hold an aircraft in the line-up position for departure on Runway 16L.
“Effective monitoring and assistance provided by air traffic control reduced the risk to both the occurrence aircraft and other aircraft in the area,” the ATSB said.
Shortly afterwards, the captain told air traffic control they had lost their primary instruments, with all of the expected navigation waypoints and tracking information not showing.
During unsuccessful attempts to restore the aircraft’s flight guidance and navigation systems, two of the three air data and inertial reference unit (ADIRU) rotary switches on the overhead panel were switched from NAV to OFF, which in response saw “several flight guidance and navigation systems degraded and the autopilot disengaged”.
After considering their degraded flight systems, the flightcrew requested a return to Sydney with a visual approach. However, bad weather meant that was not possible. Instead, the aircraft diverted to Melbourne Tullamarine with the flightcrew receiving “continuous radar vectors from the aircraft’s current position to touchdown in Melbourne”.
The captain manually flew the aircraft to Tullamarine, with the autopilot and autothrust systems becoming unavailable during the earlier attempts to restore the system, and with the aircraft’s flight control system reverting to ‘alternate law’ from ‘normal law’.
The flightcrew was then forced to conduct a go-around after coming in too high and too fast for the first attempt to land at Tullamarine’s Runway 16.
The aircraft spent about three hours on the ground at Tullamarine, where its systems underwent “extensive troubleshooting” by ground engineering services.
“This included swapping around of the ADIRUs and powering down the entire FMGS to try and replicate the situation encountered by the flightcrew.” the report said.
“No faults were found.”
With the same pilots and cabin crew, the aircraft then departed safely for Kuala Lumpur.
“This occurrence highlights that even experienced flightcrew are not immune from data entry errors. However, carrying out procedures and incorporating equipment upgrades recommended by aircraft manufacturers will assist in preventing or detecting such errors,” the ATSB said.
“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 ATSB said Malaysia-based AirAsia X conducted an internal investigation following the incident and reviewed “the recovery procedures to be undertaken in the form of a flight safety notice”.
The low-cost carrier also developed a training bulletin and package for its flightcrews that “emphasised the correct operation and alignment of the air data and inertial reference system”.
AirAsia X said in a statement on Wednesday it had taken corrective actions immediately following the incident, including equipping all aircraft with the upgraded flight management systems.
Further, the low-cost carrier said it had passed the International Air Transport Association Operational Safety Audit and the safety of its passengers are crew was its “utmost priority at all times”.
“AirAsia X would like to stress that we have in place robust management systems to monitor and prevent similar incidents from reoccurring,” the airline said.
“We remain committed to ensuring our compliance to all safety and security regulations.”
It is not the first time AirAsia X has come under the scrutiny of the ATSB. The agency is also investigating a July incident where an AirAsia X A330 and Jetstar A320 flew too close to each other near Gold Coast Airport, while in February an A320 operated by affiliate Indonesia Air Asia flew too low on approach to landing at Perth Airport.