The pilot and passenger of a Robinson R22 helicopter were conducting an aerial inspection and cattle mustering flight. During the flight, cattle were observed outside the fenced area and the pilot descended the helicopter to direct the cattle back towards the fence. The passenger then directed the pilot to fly the helicopter along the eastern fence to check its security. The passenger reported that the pilot had just commenced to climb higher, at his request, when the helicopter collided with a single-wire powerline. Recorded Global Positioning System data indicated that the helicopter struck the powerline at a speed of 55 kts. The wire did not break and the helicopter pitched nose down. The main rotor severed the tail boom and the helicopter collided with the ground 69 m beyond the powerline. It impacted in an inverted attitude, facing back along its direction of travel and rolled forward onto its left side. There was no evidence of fire in-flight or after the impact.
The main rotor, mast and upper right side of the helicopter cabin took the main impact and the mast was partially driven into the cabin. The pilot, who occupied the right seat, received fatal injuries. The passenger, although seriously injured, walked 200 m to a track and waited almost 2 hours until found by a passing motorist. The passenger reported that injury prevented him from picking up and activating the portable Emergency Locator Transmitter that was ejected from the helicopter cabin.
The powerline supplied electrical power to a nearby property and was aligned approximately east-west at right angles to the helicopter's flight path. It spanned a distance in excess of 500m from a pole in a saddle on a ridge east of the fence, to another pole set among trees in a timbered paddock. Strike marks on the wire indicated that the helicopter had struck the powerline at approximately mid-span. There were no markers on the powerline. Australian Standards (AS 3891.1-1991) specified markers on powerlines where the height of a cable exceeded 90m. The powerline did not exceed that height and at the point of contact was about 20m above ground level (AGL).
The pilot held a current Commercial Pilot Licence (Helicopter) and was appropriately qualified for cattle mustering operations. He held a valid Class 1 medical certificate and did not require any vision correction. An article on the visual aspects of wire detection by Dr Gordon Cable in the Directorate of Flying Safety-Australian Defence Force's special wirestrike edition (1997) of their safety journal "Spotlight" stated that under ideal conditions, the human eye can resolve detail down to an angle of 30 seconds of arc. That equated to being able to see a 5 mm thick wire from a distance of 150 m. However, contrast between the wire and the background against which it is viewed and the medium through which it is viewed, affect detection. The pilot was wearing a helmet with tinted visor. The fragments of perspex from the helicopter's windshield did not show any sign of being scratched or crazed.
The operator's Operations Manual required pilots to familiarise themselves with the area to be mustered, including any obstructions, before commencing mustering operations. Although the passenger had engaged the operator on previous occasions for the same work, no map of the area to be mustered was held on the operator's file. The passenger was aware of the existence of the powerline and stated that on previous occasions some pilots had him draw a "mud map" on the ground to indicate the area to be mustered, including powerline hazards. The pilot had reportedly not asked the passenger about any powerline hazards prior to the flight. There was no evidence that the pilot had previously flown over or inspected the area to determine the presence of hazards.
It is possible that the pilot may have intended to initially conduct an inspection flight to locate the missing cattle, however, after locating the cattle the nature of the flight changed to a mustering role and safety precautions normally carried out prior to mustering operations were not taken.
Visual cues, such as power poles, assist in the detection of wires. In this instance, the poles would have been partially obscured to the pilot's view by terrain and trees. Additionally, the angle subtended by the widely spaced poles would have placed them more towards the pilot's peripheral vision where they would have been less likely to be noticed.
The only visual cue to the pilot would have been the single-wire conductor. Even in bright sunlight conditions, a conductor dulled by oxidation would not have been readily discerned. In order for the pilot to have seen and avoided the powerline, he needed to be at the correct focal distance and looking directly at the wire.
Pilots operating at a low height should not rely on being able to see a powerline in time to take avoiding action.
The pilot was probably not aware of the existence of the powerline hazard.
The helicopter departed from the pad outside the operator's hanger at Mt Isa aerodrome at 1048 EST. The helicopter tracked west through the low ridge before detouring south, then turning north to the stockyards where the pilot landed to board the property manager. It remained on the ground for approximately 3 minutes before departing north east to conduct a search on a north west heading along the North Branch of Spear Creek. From there the helicopter turned left and tracked south east to a position east of the ridge. The helicopter then tracked south for approximately 3 km. It then turned right, onto a reciprocal heading, and tracked north to Spear Creek. It followed the creek north west for a short distance before turning further left to track south west back to the stock yards. The helicopter then manoeuvred around the sockyards before turning and tracking south along the western edge of the low ridges. The helicopter collided with the powerline, 5.5 km southwest of the aerodrome, at 1113.
|Date:||25 April 2002||Investigation status:||Completed|
|Time:||1113 hours EST|
|Location:||5.5 km SW Mount Isa, Aero.|
|Release date:||15 November 2002||Occurrence class:||Operational|
|Report status:||Final||Occurrence category:||Accident|
|Highest injury level:||Fatal|
|Aircraft manufacturer||Robinson Helicopter Co|
|Type of operation||Aerial Work|
|Damage to aircraft||Destroyed|
|Departure point||Hazlington Station, QLD|
|Departure time||1055 hours EST|
|Destination||Hazlington Station, QLD|
|Role||Class of licence||Hours on type||Hours total|