On 10 February 2010, ZK-TZR, a Cessna 208 Caravan aeroplane, had just taken off from Nelson Aerodrome, New Zealand on a scheduled commercial flight to Wellington when the pilots noticed a reduction in engine performance and a strong smell of fuel in the cabin. There were 2 pilots and 4 passengers on board at the time.
The pilot contacted the aerodrome controller and arranged for the flight to return to Nelson; he did this without declaring an urgency or distress situation. The aeroplane made a successful landing back at Nelson, with the engine still operating on reduced performance. There were no injuries and no damage to the aeroplane.
The NZ Transport Accident Investigation Commission found that the reduction in engine performance was due to fuel leaking past damaged o-rings that should have sealed fuel being delivered to the engine. The o-rings had been damaged by movement of the fuel-transfer tubes, which had been reduced in size at some time during maintenance by a chemical milling process that had removed the anodic protective coating.
The Commission also determined that the pilots should have declared an urgency or distress situation to ensure that emergency services were on standby in the event of a different outcome.
The Commission also found that the Civil Aviation Authority of New Zealand (CAA) system for classifying accident and incident notifications needed reviewing, because the potential seriousness of the defect that led to the forced landing, while initially recognised, was incorrectly classified and not assigned for investigation until 2 months after the Authority was first notified.
Actions taken by the CAA to address the safety issue regarding the classification of occurrences meant that no recommendation was required to be made. A recommendation was made to the Director of Civil Aviation regarding the use of correct radio telephone phraseology in the event of an emergency.