It was the first of several errors the flight crew made that day, according to the report (PDF) the Australian Transport Safety Bureau
Faulty earmuffs prompted the captain and the first officer to swap their preflight duties. The captain usually conducts an external inspection, while the first officer remains in the cockpit to complete preparation procedures.
When manually entering the coordinates of the plane’s position, the pilot incorrectly entered the longitude from a sign outside the cockpit window as 01519.8 east (15 degrees 19.8 minutes east) instead of 15109.8 east (151 degrees 9.8 minutes east), the report said.
“This resulted in a positional error in excess of 11,000 kilometers (6,835 miles), which adversely affected the aircraft’s navigation systems and some alerting systems,” the report said.
The crew had “a number of opportunities to identify and correct the error,” the report said but didn’t notice the problem until after the plane became airborne and started tracking in the wrong direction. Several message alerts and sounds suggested the error before takeoff, but the crew ignored them, according to the report.
Once the captain and the first officer realized the mistake, they tried to fix the system. But it was too late.
“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 system,” the report said.