A Robinson R44 helicopter pilot’s timely actions in conducting a forced landing after a connecting rod separated from the crankshaft while in flight near Tindal in the Northern Territory ensured a safe outcome, an ATSB investigation report highlights.
The R44 sustained minor damage during the 11 June 2025 incident, after its pilot encountered severe airframe vibrations during a personal transport flight from Daly Waters to Wally’s Airstrip. Fortunately, both pilot and passenger were uninjured in the hard forced landing into an area of open farmland.
The ATSB’s investigation established that the engine’s number 4 connecting rod had separated from the crankshaft after the nuts connecting it loosened while the helicopter was in use.
While several scenarios for this in-service loosening were considered, including abnormal loading or vibration, variation in thread condition and lubrication, improper or defective parts, microscopic deformation, and inadequate installation torque, the specific cause could not be determined.
The investigation did find that during the most recent overhaul of the engine, the independent inspection of the relevant section did not involve a physical torque check of the connecting rod nuts – although there was no indication that this contributed to the engine failure.
“While such a check was not a regulatory requirement, this did represent a missed opportunity to positively verify the installation torque,” ATSB Director of Transport Safety Dr Stuart Godley said.
Separately, the engine examination identified the helicopter’s maintenance provider had not used new gaskets when refitting the spark plugs, as required by the engine and spark plug manufacturer.
“While not found to have contributed to this incident, this observation led to the discovery of an inconsistency in Civil Aviation Safety Authority guidance,” Dr Godley said.
CASA’s airworthiness bulletin for spark plug care, AWB 20-001, stated annealed gaskets could be used during spark plug fitment, while an airworthiness bulletin specific to piston engine spark plug insulator cracking, AWB 85-023, stated new gaskets must be used in all circumstances.
“This inconsistency could have led to incorrect procedures being performed which were not in accordance with spark plug maintenance requirements,” Dr Godley said.
CASA has advised that AWB 20-001 will be cancelled, and AWB 85-023 will be amended to reflect current recommendations.
In addition, the helicopter maintainer advised new spark plug gaskets are now fitted each time spark plugs are reinstalled.
Dr Godley said the successful outcome after the unexpected engine failure event highlighted the importance of managing inflight anomalies through a comprehensive understanding of systems, and the correct application of emergency procedures.
“The pilot’s timely actions following the onset of the vibrations ensured a safe outcome,” he said.
“The incident also emphasises the importance of independent inspection of completed work to provide additional assurance that manufacturer requirements have been adhered to when installing aircraft components.”
Read the final report: Engine failure and forced landing involving Robinson R44, VH-OOE, 13 km south of Tindal Airport, Northern Territory, on 11 June 2025