What happened
The pilot had completed the landing and was preparing to deplane six passengers. To facilitate this process, the pilot reduced both the engine and main rotor revolutions per minute (RPM) to flight idle settings. During this phase of ground operations, the rear landing gear rear cross tube experienced a structural failure. The loss of integrity in this component caused the helicopter to roll over onto the helipad surface.
The investigation
Examination of the failed component revealed that the fracture surface exhibited signs of corrosion. This material degradation was identified as the primary mechanism leading to the structural collapse of the cross tube during the weight transfer associated with the RPM reduction.
Findings
The accident investigation highlighted a critical gap in the maintenance protocol for this specific aircraft model. Inspection procedures mandated that these cross tubes be examined at 100-hour intervals. However, the presence of significant corrosion on the failed part suggests that the damage had progressed beyond what would typically be detected or prevented by the existing schedule. The manufacturer is currently re-examining these inspection procedures to determine if the interval needs adjustment to better capture this type of degradation.
Safety message
Maintenance intervals must be rigorously evaluated against actual wear patterns. If corrosion is found on components that should have been inspected, it indicates a potential flaw in the detection methodology or the frequency of checks.