A transmission conductor is not a wire. It is a heavy cable, and across a span like this it weighs a couple of tons.
No drone made is going to carry that.
Which sounds like the end of the idea, and it is not, because nobody flies the conductor.
What crosses the gap first weighs about as much as a bag of shopping.
Everything heavy comes afterward, pulled through from the ground.
So the question is not what a drone can lift. It is what it has to.
Each rope pulls the next one up in size
Line stringing works as a chain of substitutions.
The aircraft carries only a pilot line, a few pounds of very strong, very thin cord, and lays it from one tower to the next.
That cord is then tied to a heavier draw rope and used to pull it across. The draw rope is tied to the conductor and pulls that.
Three stages, each one hauling the next, and only the first has to fly.
The part that makes it work is what happens at the two ends. A powered puller sits at one tower and a tensioner at the other, and between them the conductor is held in the air under controlled load for the whole crossing.
It never touches rock, water, road or fence, because it is never slack.
The drone is not a lifting machine in this arrangement at all. It is a threading needle.
The gorge and the two jobs in it
The site is Burrinjuck, in the hills near Yass in New South Wales, on an existing high voltage line.
The work came in two parts, and only one of them is the photograph everybody remembers.
The first was ordinary rope stringing between structures across steep, broken, rocky ground, the kind of terrain where walking a line in is slow and unpleasant and running a vehicle is out of the question.
The second was the crossing: a single span of about half a mile over the gorge.
The two ends are not level with each other. Between the substation and the structure on the far side the ground falls away by roughly 650 feet.
So the line is not just long. It is steeply raked, which changes how it hangs and how it has to be tensioned.
What is actually on the record
The job was reported in May of 2020, by the network operator together with a drone contractor brought in for the method.
The operator’s senior program manager for lines put it plainly afterward, saying it was especially pleasing to see the works completed without incident, which is the sentence that matters in a trade where the alternative involves flying low over rock.
On the ground the puller and tensioner used with this system are rated at about 1.5 tons.
The longest single span the same method has flown is not this one. That record stands at roughly 4,600 feet, well over three times the Burrinjuck crossing.
The contractor now reports more than 2,000 miles of line strung across upward of 40 projects in four countries, on circuits up to 765 kilovolts.
It raised 91 million dollars in late 2025 to scale the approach.
Two numbers that get used wrongly
The 650 feet is a vertical figure. It is the height difference between the two ends, not the width of anything, and it turns up regularly as though it described the gap the drone crossed.
The gap it crossed is the half mile.
Pulling capacity is the other one. Figures in the hundreds or low thousands of pounds get attached to the aircraft, when the rating belongs to the winch on the ground.
The drone’s own load is the pilot line and nothing else, and that distinction is the whole reason the method works.
Weights quoted for the aircraft itself also circulate without a source, which is worth remembering before repeating them, in the same way that headline figures around a heavy lift or a long crossing tend to outrun the paperwork.
What the method actually replaces
The alternative is a helicopter, and it is a real one that still gets used on big projects today.
A helicopter can carry far more and works fast, but it costs a great deal per hour, it is loud over country where people live, and it puts a pilot at low level between towers in terrain with no landing options.
A drone removes the person from that part of the job entirely.
It also removes the need to cut access, because nothing has to drive to the far side, as the operator’s account of the work sets out.
Six years on, the two methods run side by side on the same projects rather than one replacing the other, as the agency writeup of the system describes.
The pilot rope was never the difficult part of stringing a line.
Getting it to the other side always was.
