On 31 October 2021, a "Fuel Imbalance" message occurred on a Boeing 787-9 soon after departing Bangkok at night but attempted fuel transfer was unsuccessful. A "Fuel Disagree" message subsequently appeared, and use of available system checklists indicated that there was a fuel leak from the left engine or tank. Left engine shutdown was therefore accomplished and a MAYDAY diversion to an overweight landing at Goa, India, followed. The Investigation determined that the leak was actually from the right fuel tank and attributed crew misdiagnosis to limited fuel system malfunction checklists and gaps in crew guidance and training on fault diagnosis.