According to The Guardian, "a combination of data entry errors, crew ignoring unexplained chimes from the computer system, and bad weather in Sydney" led to the Airbus A330 landing in Melbourne just after 2pm, some three hours after take off on March 10 last year.
The publication also noted that while the Melbourne airport is 722km southwest of Sydney, Kuala Lumpur is 6,611km northwest.
Citing the findings of the Australian Transport Safety Bureau (ATSB) published today,Guardian said the problem occurred when faulty earmuffs prompted the captain and first officer to swap their usual pre-flight checks.
"Ordinarily, the (ATSB) report said, the captain would conduct an external inspection of the plane while the first officer stayed in the cockpit and, among other tasks, completed the position initialisation and alignment procedures.
"On this day, however, the captain's ear protection was not available so he took over the cockpit tasks, which included entering their current coordinates, usually given as the coordinates of the departure gate, into the plane's internal navigation system."
The ATSB found that the captain manually copied the coordinates from a sign outside the cockpit window into the system, and that later analysis showed a "data entry error".
Instead of entering the longitude as 151̊ 9.8’ east, or 15109.8 in the system, the pilot incorrectly entered it as 15̊ 19.8’ east, or 01519.8.
"This resulted in a positional error in excess of 11,000km, which adversely affected the aircraft's navigation systems and some alerting systems," Guardian quoted the ATSB.
However, the ATSB also noted that the crew had "a number of opportunities to identify and correct the error" but did not notice it until they had become airborne and started to track in the wrong direction.
"Those opportunities included a flag or message that flashed up on the captain's screen during crosscheck of the cockpit preparations, which the first officer later told ATSB investigators he had seen but not mentioned because it was 'too quick to interpret'; and three separate chimes which, because they were not accompanied by a message from the computer, were ignored.
"A fifth sign that something was wrong came in the form of an alert blaring: "TERRAIN! TERRAIN!" This was not ignored – both pilots said it had 'startled' them. But, as that alert meant they were about to hit something and they could see the way ahead was clear, and as the busy runways at Sydney airport made the full response to such an alert 'undesirable', they pressed on," said Guardian.
However, when the autopilot was engaged at 410 feet, it tracked the plane moving left, toward the flight path of another runway.
According to the ATSB, when the captain and first officer tried to fix the system, it "resulted in further degradation of the navigation system, as well as to the aircraft's flight guidance and flight control systems".
Following this, the pilot requested to return to Sydney and informed the air traffic control that only a visual approach was possible, which is to land the aircraft without the assistance of the navigation system.
As the weather conditions had worsened in Sydney, air traffic control had advised the pilot to head to Melbourne.
In Melbourne, three hours was spent on fixing the problem and the plane arrived in Kuala Lumpur at 10.20pm, six hours behind schedule.