The Australian Transport Safety Bureau (ATSB) has urged operators and maintainers to pay careful attention to critical components after cracks were found in the fanwheel of a crashed Robinson R22.
VH-YMU was hovering 60 feet AGL near McArthur River mine, NT, in August 2020 when the engine lost power and the aircraft crashed heavily. The pilot was seriously injured in the impact and the aircraft substantially damaged.
An ATSB investigation report released this week found evidence of fatigue cracking in the helicopter’s cooling fanwheel outer support ring, and in the welded region of two vanes of the fanwheel assembly.
“These fatigue cracks probably weakened the fanwheel structure sufficiently for it to break-up in flight,” said ATSB Director Transport Safety Stuart Macleod.
This ATSB believes an ensuing imbalance likely led to the forward drive belt coming off the sheaves, resulting in a loss of rotor drive.
According to the ATSB, cracks have been found in Robinson fanwheels before, but they believe this was the first instance where the cracking had progressed to the point of in-flight failure.
The conclusions prompted Macleod to issue a warning about the importance of inspecting critical components.
"The circumstances of this accident are an important reminder for pilots and maintainers to pay particular attention to the installation, maintenance, and ongoing inspection of critical components of the drive systems of both Robinson R22 and larger R44 helicopters,” he said.
Many Robinson operators are aware that cracking can occur at the welded regions of the cooling fanwheel, but Macleod said instances of cracking needed to be reported.
“This awareness, however, is not reflected in CASA’s Defect Reporting Service data, suggesting such instances are under-reported,” he stated.
“The non-reporting of defects prevents the sharing of knowledge to the wider aviation community and the identification of emerging issues.
“Defect reporting benefits the aviation industry. It allows CASA to create a database, which is used to identify trends in design and maintenance reliability of aircraft systems and components and is a publicly accessible service.”
The full investigation report is on the ATSB website.