CHICAGO - Zac Vawter considers himself a test pilot.
The 31-year-old software engineer is helping to test a bionic prosthetic leg that's controlled by his thoughts.
He'll put it to the ultimate test Sunday when he tries to climb 103 flights of stairs to the top of Chicago's Willis Tower.
It's one of the world's tallest skyscrapers.
After losing his right leg in a motorcycle accident, Vawter signed up to become a research subject. If all goes well, he'll make history with the bionic leg's public debut.
The robotic leg will respond to electrical impulses from muscles in Vawter's hamstring.
He'll will think, "Climb stairs," and the motors, belts and chains in his leg will synchronize the movements of its ankle and knee.
Vawter hopes to make it to the top in an hour.
That's longer than it would've taken before his amputation, but less time than it would take with his normal prosthetic leg.