Robinson R22 Beta, VH-AVE, Bundubaroo Station, 170 km south of Charters Towers, Queensland

FACTUAL INFORMATION

History of the flight

The pilot had commenced mustering at about 0700 EST. At about 1030 the aircraft was refuelled to full tanks during a "smoko" break. The pilot's intention was then to muster about 30 head of cattle which had been separated from the main mob. The pilot had agreed to take a passenger on the flight which was expected to be of relatively short duration. The passenger had been holidaying at the property and was keen to experience a helicopter flight.  The helicopter became airborne at about 1050 and was last heard at 1115. At 1130 a jillaroo realised she could no longer hear the helicopter and began making enquiries on a hand-held radio. When nothing was heard, she began a search on a trail bike and eventually discovered the wreckage and the deceased occupants at about 1420.

Impact sequence

The tail rotor had struck the top branches of a lone 7-metre-high sapling, causing one blade to separate. The tail rotor gearbox then separated, and the main rotor struck the tail boom. The wreckage fell to the ground 30 metres beyond the sapling. The right side of the cabin was crushed. There was no fire.

Wreckage examination

The cabin was crushed on the right (pilot's) side by ground impact. The Perspex bubble was scattered in front of the main wreckage, which was facing south-south-west. The main rotor blades showed evidence of having struck the tail boom and the cabin structure. The tail rotor drive shaft was recovered and showed evidence of torque twisting, indicating that the tail rotor drive shaft was being driven under power when the tail rotor contacted the tree.

The left side of the passenger seat with the seat lap belt attachment, had detached from the fuselage structure and this allowed the passenger to strike the upper door frame during impact. The control systems were examined and appeared to be functioning normally. The engine governor switch in the end of the collective control was found in the off position.

The engine was removed and examined. There were no defects found which would have precluded normal operation.

Weight and balance

The weight and balance of the helicopter was within the limitations published in the aircraft flight manual.

Emergency locator transmitter (ELT)

The Ack Technologies ELT was found undamaged in the mounting bracket at the rear of the engine bay. The arming switch was found in the off position.

ANALYSIS

Civil Aviation Regulation Section 29.10 states that during aerial stock mustering operations, a pilot shall not carry more than one other person and that that person must be essential to the successful conduct of the operation. In this case, the passenger was not essential to the conduct of the operation. The helicopter had been refuelled to full tanks immediately before the flight and, although within the specified weight limitation, it was much heavier with the additional weight of the passenger than the pilot was accustomed to for mustering. Although the pilot was highly experienced, the resultant reduction in performance may have been a factor in his being unable to avoid the collision with the tree.

There were no witnesses to the accident and the final flight path before the collision with the tree could not be determined. However, it was evident that immediately after the tree was struck by the tail rotor, the helicopter was subjected to violent manoeuvres.

The RPM governor is fitted to the engine to prevent decay of rotor RPM when manoeuvring. The aircraft flight manual states that flight is prohibited with the governor switched off, except when there is a system malfunction or for emergency procedures training. The governor switch was found in the off position, but it may have been bumped to this position in the accident sequence. If it was deliberately switched off for the flight, manoeuvring performance of the helicopter may have been reduced.

The possibility that the pilot may have been attempting a precautionary landing for some reason such as an engine malfunction, was considered. There was no evidence found to substantiate such a possibility.

SIGNIFICANT FACTOR

The tail rotor struck a tree, and this precipitated a major structural failure. Why the pilot was unable to avoid the tree could not be determined.