Norwegian accident investigators have urged the country’s civil aviation regulator to review its policy on the marking of overhead powerlines after a light helicopter narrowly avoided a crash after flying into an unmarked cable.
Disclosing its findings into the 6 September 2021 event, the Norwegian Safety Investigation Authority (NSIA) says that only luck and the pilot’s airmanship prevented the incident from “becoming a serious accident”.
In the event, the helicopter snared a cable on its right-hand skid, dragging it onto a parallel cable and shorting the power, before the momentum of the rotorcraft forced its nose down into a position where a main rotor blade cut the wire.
“In the NSIA’s opinion, small margins and coincidence are to thank for the cable first hitting the helicopter between the fuselage and the skids instead of hitting the rotor system. Had the cable hit the rotor system, the outcome would very likely have been catastrophic,” it says.
In addition to the poor visibility of the unmarked powerline – spanning the Gullesfjord in northern Norway – the NSIA attributes the collision to failures by helicopter operator Heli-Team, the pilot’s inexperience in conducting line inspections, and resulting high mental workload during the mission.
Heli-Team had been contracted by powerline operator Vestall – then known as Vesteralskraft Nett – to perform visual inspection of pylons and pole tops in the Sortland area and had deployed an Airbus Helicopters H125 (LN-ORJ) for the mission.
While the helicopter pilot received some information on the assignment on 3 September, the final confirmation was only sent “late on his day off” – the day before the inspections were due to be conducted. Around 1h was spent on planning the mission, the pilot told the inquiry.
The cables to be inspected ran down either side of the fjord but intersected with powerlines – both at 22kV – spanning the water on a northwest path as it curves to the north. These consisted of three separate aluminium-wrapped steel cables, each with a tensile strength of 19.6t.
But he assumed that both 22kV lines “would be the same height and that the flight would therefore be safe with regard to passing the overhead powerline”, the NSIA states.
In addition, marked powerlines belonging to another operator, Statnett, were also strung across the fjord, running roughly parallel 400m (1,310ft) to the west.
Black and white maps provided by Vestall “only showed the power company’s own powerlines” – those of other operators were absent.
Nonetheless, the two lines were identified by the helicopter pilot as part of his pre-flight safety analysis.
As meteorological data for 6 September indicated a southerly wind, the inspection was to be flown from north to south. The cloud base at the time was between 800 and 3,000ft, falling to 400-800ft during periods of precipitation, while visibility varied from 2nm (4km) to more than 5nm, reducing during rain showers.
During the inspections, the helicopter would fly parallel to the cables, allowing the two Vestall engineers aboard to identify faults. Each time an issue was identified “the commander did a 360° turn” to allow the power company staff to “document it more thoroughly”.
Approaching the powerline crossing the fjord, the engineers observed another fault on the crossarm of an electricity pole. At this point the flight also “became more demanding” encountering light rain and rising terrain to the left of the aircraft.
As the pilot began executing another 360° right-hand turn at around 40-60kt (74-111km/h) the helicopter “passed under the powerline without the commander noticing”, says the report. It then climbed slightly before “switching to a downward turn”.
“While making the turn, the commander suddenly noticed the overhead power line spanning the fjord and instinctively pulled up the collective pitch control to avoid a collision. Shortly after, the helicopter’s right skid caught in the middle cable and lifted it over the northernmost cable.”
This caused the helicopter to pitch down at around 90°, the pilot stated, causing one of the three main rotor blades, around 27cm from the tip, to strike the middle cable, severing it. The aluminium wires surrounding the cable’s steel core were also torn off and were left “wound around” the skids.
Despite initial fears that the H125 had become uncontrollable, the pilot was able to perform an emergency landing on nearby marshy ground.
Although the power company employees “considered whether the power cable now lying on the ground could be live”, they concluded “that the live part of the cable would be in the sea”.
Neither the pilot nor the three passengers were injured in the incident.
Both sets of powerlines crossing the fjord had been “reported as obstacles to aviation”, say the inquiry, “but only Statnett’s line has been physically marked”.
In fact, Vestall had in 2010 had asked the Norwegian civil aviation agency (CAA) for, and had been granted, an exemption from the requirement to mark the powerlines, noting that 90m of the line was more than 60m above sea level and that Stattnett’s adjacent line was marked.
“CAA Norway concluded, without much justification, that the power line spanning the fjord did not constitute an obstacle to aviation,” says the NSIA.
The regulations covering the line marking were updated in 2014 and 2023, defining all “signal-carrying and live overhead powerlines, regardless of altitude” as an aviation obstacle.
While there is an exception for powerlines where “less than a continuous section of 100m is above the height subject to the marking obligation”, the rules also stipulate marking where lines are “to be inspected by manned or unmanned aircraft” and cross under other high-voltage cables.
“The marking must be clearly visible to aircraft during line inspections to make them aware, when flying along power lines, that they are approaching crossing overhead lines. Each side of the crossing overhead power line must be marked”.
Markings must “in daylight, be visible at a distance of at least 1,500m from all relevant approach angles”, the regulations state.
Additionally, a previous incident in 2018 when a helicopter struck overhead cables in similar circumstances, had prompted the NSIA to recommend the marking of crossing powerlines. If that proposal had been enacted at the time of the incident “the commander would most likely have noticed and avoided [the] overhead powerline”, it says.
It has called on the Norwegian CAA “to reconsider its conclusion and consider whether the overhead powerline spanning the Gullesfjord should be physically marked.”
The CAA should also “follow up overhead powerlines that are exempt or partially exempt from the marking obligation in order to verify that they are marked in accordance with the new regulations”.
Since the incident, Heli-Team has updated the maps installed on its iPads and modified its operating procedures related to the use of more detailed charts. Procedures and risk assessments around line inspections have also been tightened.
“It is the NSIA’s assessment that the maps on the company’s iPad and in the commander’s ‘memory’ regarding places and locations were the final safety barriers meant to prevent conflict with the overhead power lines spanning the fjord,” says the agency.
“Human barriers are generally considered weak safety barriers, as this incident also confirms.”
