An AirAsia flight from Sydney to Malaysia ended up in Melbourne instead when the pilot entered the wrong coordinates into the internal navigation system, an air safety investigation has found.

The Airbus A330 was scheduled to leave Sydney international airport at 11.55am on 10 March 2015, and arrive in Kuala Lumpur just under nine hours later.

Instead, through a combination of data entry errors, crew ignoring unexplained chimes from the computer system, and bad weather in Sydney, it landed in Melbourne just after 2pm.

Melbourne airport is 722km southwest of Sydney. Kuala Lumpur is 6,611km northwest.

According to a report by the Australian Transport Safety Bureau (ATSB) published on Wednesday, the problem occurred when faulty earmuffs prompted the captain and first officer to swap their usual pre-flight checks.

Ordinarily, the 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 report said 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 151° 9.8’ east, or 15109.8 in the system, he incorrectly entered it as 15° 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,” the ATSB said.

The report said 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.

However, when autopilot engaged at 410 feet, it tracked the plane left, toward the flight path of another runway.

Both the captain and the first officer tried to fix the system but “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 ATSB said.

They requested to return to Sydney but told air traffic control they were were only capable of making a visual approach – that is, landing without the assistance of their navigation systems.

Air traffic control replied that since the weather and visibility had worsened in Sydney, they should instead head to Melbourne.

The plane spent three hours on the ground in Melbourne fixing the problem before departing for Kuala Lumpur, where it arrived at 10.20pm local time, six hours behind schedule.

The ATSB said “even experienced flight crew are not immune from data entry errors” and advised AirAsia to upgrade its flight systems to assist in preventing or detecting such errors in future.

Air Asia said it upgraded its flight management systems on its Air Asia X planes, sent a training bulletin to staff emphasising the correct operation and alignment of the flight data system, and had briefed all pilots on the findings of its internal investigation.

“AirAsia X would like to stress that we have in place robust management systems to monitor and prevent similar incidents from reoccurring,” it said in a statement on Wednesday.

“We also wish to reiterate that we have regularly passed safety and security audits conducted by various international regulators, including the IATA Operational Safety Audit. We remain committed to ensuring our compliance to all safety and security regulations.”