What happened
During maintenance on the aircraft registered VH-JFU, the right engine was reinstalled with two critical oil lines incorrectly connected. Specifically, the air/oil cooler return line and the air/oil separator vent line were transposed. This error persisted throughout 68 hours of flight time, during which the engine sustained damage to the reduction gearbox scavenge pump housing. This damage was not identified during subsequent maintenance activities following the initial error.
The investigation
Investigators found that the error was possible because the two flexible lines were adjacent, used identical fittings, and were of the same size. Because the same spanner could be used for both, there was no physical hindrance to misconnecting them. While the engine manufacturer had previously issued service information letters regarding this risk, the specific markings on the oil tank intended to guide correct installation had worn off. Consequently, there was no visual prompt for the engineers to verify the orientation of the lines. The error went undetected by both the technician performing the installation and the certifying engineer, as the required independent inspection protocols did not specifically mandate a check of these oil lines.
Findings
- The air/oil cooler return line and the air/oil separator vent line were swapped during engine installation.
- The physical similarities between the two lines, including identical fittings and proximity, facilitated the unintentional transposition.
- The absence of visible markings on the oil tank due to wear removed a critical visual safeguard.
- Post-occurrence maintenance failed to detect damage to the reduction gearbox scavenge pump housing.
Safety message
Operators and maintenance personnel should consult with the engine manufacturer regarding technical advice for non-routine issues. This is necessary to ensure that non-normal configurations are fully identified and rectified before an aircraft is released to service.