What are those orange or white balls that hang on power-lines above random roads?

”...no airplane would ever be that low…”
I’ve only seem them near airfields, so I think they are indeed aircraft warnings. Usually (in my experience) these markers are associated with smaller, general aviation landing strips, not commercial airports.

@gasman That’s what I thought for a long time. What part of the country are you in? I noticed that when I thought about it, I have never seen any in Colorado, where I live now. But when I went back to PA, they’re fairly common. And as I was noticing yesterday, where I was driving on a dinky back road, there was no airfield and I don’t think there ever had been near any of the places I saw them. Most were in densely wooded rolling hills. Not very flat at all. So maybe they are just extremely outdated, but you’re right and they were for airfields at one point? That might explain why ya don’t see them out west?

@deni I’m in western WA state. You see those orange balls on power lines near Boeing Field (general aviation) but not Sea-Tac International. I used to live in rural GA and TN, where I also saw them near small air fields. I wonder if they’re mandated by FAA?

@gasman : Way back in the day they had those near Issaquah when they had the glider fields there. It may well be for small low-flying aircraft, crop-dusters, etc.

They are landing notes for helicopters.

They are generally placed for high visibility for pilots who “may be” flying aircraft (including fixed wing and rotor craft – helicopters) in all kinds of applications, including crop dusting, rescue landings (for helicopters) and even inspection of the power lines themselves, which is often done from the air. This would explain why the balls are often placed near roadways and other places where “airplanes” wouldn’t normally land – but helicopters might, for one reason or another.

In addition to human pilots, the balls often are placed in areas where migratory bird routes may intersect them. Apparently, having the balls in place in areas near migratory bird routes (and near wetlands landing areas for wetland birds) reduces bird wire strike mortality by up to 50%. (You could google to find the same links that I did on this. I have no more faith in them than I do in any other random link I find.)

I also speculated (and I seem not to be the only one guessing at this) that there may be a mechanical reason, as well. Winds of a certain speed (not always “high winds” necessarily) could possibly set up destructive vibrations in the wire parabolas, and having the balls in place disrupts what could be a dangerous harmonic. I didn’t find links to verify that, but it makes some sense to me.

The balls are warning devices for low-flying aircraft, like helicopters.

They’re not for birds to land on?

Generally everywhere you have some kind of air traffic, you can see them. Besides airplanes, this can include helicopters, microplanes, paragliders, base jumpers. Check if there’s an airfield or a helicopter landing site near the location.

I would think they would be applicable only to light aircraft, which often fly lower and follow roads for navigation. Your average long-haul passenger jet isn’t going to be flying low enough to snag power lines.

While the question has received accurate and satisfying answers, this photo may help folks unfamiliar with the orange balls. According to the caption this was taken next to a hospital helicopter pad.

They are for low flying, crop dusting planes. You will often see them when the road passes between two fields of the same crop, although that is not a necessity.