The ATSB has released a Safety Advisory Notice to Robinson R44 operators and maintainers highlighting the importance of inspecting the helicopter's clutch shaft yoke.
The Safety Advisory Notice arises from the ATSB's ongoing investigation into a loss of control and collision with terrain accident involving an R44 that was conducting aerial spraying operations near Clare, South Australia on 22 December 2020, which has identified that fatigue cracking in the clutch shaft forward yoke resulted in the total loss of drive to the main rotor system.
"The ATSB's preliminary metallurgical examination of the drive train components identified that the clutch shaft forward yoke had fractured," said ATSB Director Transport Safety Stuart Macleod.
"Corrosion product and fretting damage were identified in the vicinity of the bolt hole adjacent to the fatigue fracture surfaces."
The yoke is required to be inspected at every 100-hour, or annual, inspection, however, the ATSB's Safety Advisory Notice states that a general visual inspection of the assembled clutch shaft yoke during the 100‑hour or annual inspection may not easily identify defects such as corrosion, fretting and/or cracking.
"The ATSB advises operators of R44 helicopters to note the preliminary finding of this accident and to look for the presence of corrosion, fretting or cracking, which may not be visually obvious, during inspections of the clutch shaft yoke," said Mr Macleod.
"Any identified defects should be notified to both the ATSB and the Civil Aviation Safety Authority."
While the specific circumstances that led to the fatigue crack on the accident helicopter are still under investigation, the ATSB has issued the safety advisory notice to advise R44 operators of the potential safety concern.
Pending the publication of an investigation's final report, the ATSB may issue Safety Advisory Notices to raise awareness of safety critical concerns determined during the course of an investigation without waiting for the conclusion of the investigation.
You can find here the Safety Advisory Notice: AO-2020-064-SAN-014 R44 helicopter drive train failure
Last update 07 June 2021
