Thaddeus Shrader used to cruise the skies as an airline captain. But in 2008, he switched to a career creating new ways to soar: zip lines. He’s now the CEO for Bonsai Design, which specializes in building zip-line courses that minimize the damage to forests. “You’re flying in and out of living structures,” Shrader says. “We have to figure out a way to make the whole thing safe and legal.”

How did you go from flying planes to designing zip-line components?

I went to college for aeronautical engineering. At that time, there wasn’t a lot of work for aeronautical engineers, so I got a job as a pilot. After my wife and her brother started running this company, I came over and brought my engineering background. That’s when Bonsai really started inventing new components: new trolleys, harnesses, braking systems, and emergency-rescue devices.

Thaddeus Shrader
Thaddeus Shrader Courtesy Bonsai Design

What’s the appeal of zip lines?

This is the closest you can get to the real feeling of flight. The wind is in your hair, you’re above the ground, your wings-slash-arms are out from your side, and you’re blasting along. It’s beautiful.

Do you get to play with your designs?

We’re always trying to figure out new ways for people to fly, and we have to test all those ideas. My kids are our test monkeys. We actually develop a lot of stuff in our backyard—and we get paid to do it.

This article originally appeared in the September 2015 issue of Popular Science, under the title “Zip-Line Designer.”