On 13 August 2007, a Boeing 737-700 aircraft, registered VH-VBR, was operating on a scheduled flight from Brisbane to Hamilton Island, Qld. On reaching cruise altitude, the flight crew became aware of a fuel imbalance situation due to fuel loss from the number-2 (right) engine. At 1311 Eastern Standard Time and approximately 148 km SE of Rockhampton, Qld, the crew conducted an in-flight shut down of the right engine. The aircraft was subsequently diverted to Rockhampton where a single-engine approach and landing was completed without further incident.

Examination identified the leak as being from the main fuel return pipe where it connected into the oil/fuel heat exchanger. The pipe connection was of flanged plate design, held in position by four bolts tightened into threaded inserts on the oil/fuel heat exchanger body. The threaded inserts had failed, pulling free of the heat exchanger body.

The investigation found that the failure of the inserts was the result of over tightening that had occurred during previous maintenance. The oil/fuel heat exchanger was subject to two different modification states, each requiring different fuel return pipe bolt torque values.

As a result of this occurrence, the aircraft operator notified the subsequent maintenance provider of the incident and received assurance that their process, procedures and oversight were adequate to prevent a recurrence.