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Section 21 (2) of the Transport Safety Investigation Act 2003 (TSI Act) empowers the ATSB to discontinue an investigation into a transport safety matter at any time. Section 21 (3) of the TSI Act requires the ATSB to publish a statement setting out the reasons for discontinuing an investigation. The statement is published as a report in accordance with section 25 of the TSI Act, capturing information from the investigation up to the time of discontinuance. |
Overview of the investigation
On 15 September 2020, the ATSB commenced an investigation following notification of main rotor blade delamination involving a Robinson R44 Raven I helicopter, registered VH-RJN. The blade defect was identified on 3 April 2020 while the helicopter was undergoing maintenance at Mareeba Airport, Queensland.
In the days prior, VH-RJN was being operated from Gunnawarra Station, Queensland. On the morning of the 3 April 2020, the pilot conducted a pre-flight inspection of the helicopter. No issues were identified other than an intermittent engine starter, which the pilot/owner intended to have rectified later that day by flying the helicopter to a maintenance organisation at Mareeba Airport.
The pilot conducted an inspection of a station fence line in preparation for the arrival of cattle that were being mustered through the property. The pilot then returned to the station homestead before departing to Mareeba for rectification of the starter issue.
While en route to Mareeba, overhead the Herberton Range, the pilot reported encountering a brief period of moderate turbulence that subsided once clear of the range. The helicopter was landed at Mareeba without issue. After resolving the engine starter defect, the maintenance organisation advised the pilot/owner that during a post-flight inspection one of the main rotor blades was found unserviceable. A patch of paint had dislodged from the upper skin at the blade tip due to the development of corrosion damage at the interface with the tip cap (Figure 1).
Figure 1: Main rotor blade tip corrosion damage
Source: ATSB
During the investigation, the ATSB:
- Interviewed the pilot/owner of VH-RJN.
- Obtained the helicopter’s maintenance records.
- Conducted a technical examination of the defective main rotor blade which confirmed that corrosion had developed on the underside surface of the blade in the region of the tip cap. A small portion of the underside skin displayed evidence of minor disbonding at the intersection with the spar-to-skin bond line. The corrosion had progressed underneath a region of primer that had been applied as a protective measure against paint erosion along the leading edge of the blade.
Reasons for the discontinuation
The ATSB uses its limited resources for maximum safety benefit, and in this case there was no effect on the conduct of the flight and that the defect was discovered during a post-flight inspection of the helicopter.
The pre-flight inspection requirements for the main rotor blade are cited by the helicopter manufacturer in the Pilot’s Operating Handbook, as well as within the Maintenance Manual during the conduct of scheduled maintenance. In addition to those requirements, the helicopter manufacturer had previously released a service bulletin that was intended to reduce the likelihood of corrosion developing at the blade tips by a modification to the blade; SB-103 Main Rotor Blade Tip Plate Permanent Removal and Sealant Application. The service bulletin recommended that a plate attached between the blade tip and the tip cap be removed. In this instance the tip cap plate from VH-RJN had remained in place, which may have influenced the development of the corrosion.
A review of the available records on the CASA defect reporting database during the period 2018‑2020 determined that corrosion and associated disbonding at the blade tip has been identified in other instances. The blade damage was typically found during routine maintenance.
The evidence collected during this investigation remains available to be used in future investigations or safety studies. The ATSB will also monitor for any similar occurrences that may indicate a need to undertake a further safety investigation.