What happened
During a recent departure, a Boeing aircraft, registration VH-ZNJ, left the gate with four engine fan cowl static ports still obstructed by covers. The covers had been secured with tape in accordance with a specific procedure designed to prevent the covers' streamers from being lost in high winds. Because the tape held the streamers flush, the covers were not easily visible during standard walk-around inspections. The aircraft subsequently operated with reduced redundancy to the engine electronic control system.
The investigation
The investigation examined the maintenance and inspection processes used by the operator. It was found that while the aircraft's parking procedures were linked to Boeing's specific instructions, the instructions for restoring the aircraft to service did not provide the same level of detail. This lack of integration meant engineers did not have easy access to the necessary procedures to confirm which ports were covered. Furthermore, the operator's maintenance documentation required the ports to be covered but failed to specify their exact locations, which could lead to inconsistent interpretations among engineers.
Additional factors included the physical placement of the covers, which were located below eye level and required a deliberate downward view to detect. The investigation also noted that the flight crew and dispatcher performed inspections with a low expectation of finding anomalies, as the aircraft had already been released by engineering. A distraction involving a separate pitot cover found on the ground was also noted during the initial exterior inspection.
Findings
- The engine fan cowl static ports were not removed by engineering as required by manufacturer procedures.
- The use of tape to secure the covers significantly decreased their visibility.
- Maintenance documentation lacked specific locations for all static ports and failed to reference the necessary Boeing procedures during the restoration phase.
- The dispatcher's exterior inspection did not follow documented procedures, reducing the effectiveness of the safety check.
- Inspection bias played a role, as the crew did not expect to find uncovered ports after the aircraft had been released by maintenance.