The helicopter was conducting a private flight from a property near Mansfield, Victoria with a pilot and one passenger on board on 6 July 2019.
Before the flight, the pilot sought and obtained some information about hazards, including powerlines, from the property owner. However, the owner was not aware of a distribution powerline strung across the nearby valley with a span of 560 metres, and he could not see the wires from his property. The wires did not have aircraft markers and, in accordance with the relevant Australian Standard (AS 3891), did not require marking.
Additionally, and unlike some other states, readily usable Victorian electricity network maps were not available to assist the pilot’s planning.
As a result, the pilot’s pre-flight planning did not identify the powerline, which the helicopter struck 158 feet (48 metres) above the ground, shortly after take-off. The helicopter descended rapidly, travelling about 400 metres after the wirestrike before colliding with the ground in an upright position, and rolling over, resulting in serious injuries to the passenger and minor injuries to the pilot.
“In Victoria, electricity network information is not readily available to aid pilots during the flight-planning process,” ATSB Director Transport Safety Stuart Macleod said.
“Such information provides valuable safety information to aid pilots in planning flights, and assists the visual identification of hazards, such as wires and poles.”
It is good practice to always maintain a height of at least 500 feet above ground level.
The investigation also highlighted that when flying at low level, pilots should always be constantly scanning the terrain on either side of their flight path for poles and towers, and should avoid low flying unless it is necessary, Mr Macleod noted.
“The ability of pilots to detect powerlines depends on physical characteristics such as the spacing of power poles, the orientation of the wire, and the effect of weather conditions. Depending on the environmental conditions, powerlines may not be contrasted against the surrounding environment. In addition, the size of the wire and limitations of the eye can mean that it is actually impossible to see the wire,” Mr Macleod said.
“Therefore, it is good practice to always maintain a height of at least 500 feet above ground level except during take-off and landing.”
After the accident, local landowners advised the ATSB that the powerline was erected in the 1970s, and that an aircraft conducting aerial agriculture had struck it in the 1980s. They reported that following that past incident, orange plastic marker balls had been fitted to the wires, however, they had perished over time and not been replaced.
“Effective wire avoidance can be achieved using a combination of available wire location information; wire marking; and the avoidance of unnecessary low flying, especially flight below the height of surrounding higher terrain where wire spans may be present,” Mr Macleod reiterated.
Read the report: AO-2019-031: Wirestrike and collision with terrain involving Robinson R44, VH-KCH, near Mansfield, Victoria, on 6 July 2019