Nut loosened overtime before R44 drive belt tensioning motor failed during flight
Personnel involved in maintenance and operations of R44 helicopters should be aware of the risks posed by the failure of the drive belt tensioning motor, as demonstrated by an incident at Hamilton Island in January.
On 8 January 2023, the pilot of an R44 was on approach to Hamilton Island Airport, Queensland, when they noticed a persistent clutch warning light.
The pilot carried out the clutch warning light emergency procedure, and landed at the airport.
Ground crew found the clutch actuator electric drive motor had separated from the gearmotor assembly, and fallen between the drive belts and the right-hand fan shroud.
“A subsequent Australian Transport Safety Bureau investigation found that during assembly of the gearmotor, the required thread adhesive was either not applied, or applied in a manner that did not prevent the loosening of the electric motor retaining nut,” ATSB Director Transport Safety Stuart Macleod said.
“Consequently, over time, normal aircraft vibrations loosened the retaining nut, resulting in the clutch actuator electric motor separating from the gearmotor assembly in flight.”
Robinson Helicopter Company advised the ATSB they are working with the component manufacturer to rectify identified quality issues with the gearmotor assembly.
Robinson said it is also considering updating the procedures for the inspection of the clutch actuator assembly.
“This incident is a reminder to R44 maintainers and operators to be aware of the risks posed by the failure of this component, specifically the risk of a loose component interfering with the v-belts and impacting rotor drive,” Mr Macleod said.
“The ATSB encourages pilots and maintenance engineers to physically check the security of the R44 clutch gearmotor assembly on a regular basis.”
Additionally, Mr Macleod emphasised that any discovered defects should be rectified, and reported to the Civil Aviation Safety Authority, and the manufacturer.