• The fracture site on the separated tail of VH-NBY. (ATSB)
    The fracture site on the separated tail of VH-NBY. (ATSB)

The ATSB has this week concluded its investigation into the in-flight break-up of a Robinson R44 near Broome, determining that the aircraft crashed because the tail had sustained damage prior to the flight.

VH-NBY was being used for a private flight conducted from an industrial estate north of Broome in July 2020 when the tail rotor system broke away. The helicopter continued climbing to 75 feet AGL before control was lost, resulting in a crash that killed the pilot and one passenger, and seriously injured two other passengers.

The ATSB determined that an overstress fracture occurred in the attachment lugs of the tail rotor gearbox input cartridge, although the source of the load that caused the overstress couldn't be identified.

Prior to the accident flight, two pilots had reported an unusual vibration through the helicopter's pedals, but maintenance engineers found the tail rotor was within balance limits the day before the crash and a visual inspection revealed no defects in the tail.

Despite the MRO's recommendations for a maintenance check flight, the aircraft was returned to service without that having been done.

“As the vibration was reported to only occur in flight, and no defect was identified, it was reasonable to have concluded that the problem may still be present,” said ATSB Chief Commissioner Angus Mitchell.

“As such, the safest next step, which is recommended by the helicopter manufacturer, would be to conduct a graduated flight check of hovering then re-inspection. Preferably, this would be with only a prepared pilot on board.

“Instead, the next flight, during which the accident occurred, involved the conduct of a high‑power towering take-off from a confined area with the passengers on board.

"This accident demonstrates the importance of following a conservative troubleshooting process that minimises risk.”

Investigators also found out that the pilot did not have a current flight review for the Robinson R44, and that responses to the loss of the tail rotor did not match the procedure in the Pilot Operating Handbook for that model.

The report also singles out the aircraft owner and operator.

"The owner of VH-NBY demonstrated acts of non-compliance with multiple aviation safety regulations," investigators state in the report finding. "Additionally, VH-NBY was operated in a manner that increased the risk of damage or stress to the helicopter on multiple occasions.

"These actions had an adverse influence on safety and imposed unnecessary risk on passengers and third parties.

"Although the registered operator of VH-NBY was responsible for the continued airworthiness of its helicopter fleet, they did not employ a conservative defect resolution process that would have supported further trouble shooting."

In August 2021, the ATSB appealed to the helicopter industry to report any unrecorded reasons for damage to Robinson tail rotor gearbox input cartridges, suspecting that ground handling could result in failures such as that experienced in VH-NBY.

The full report is on the ATSB website.

comments powered by Disqus