In a sky-high drama construction workers on Saturday installed the underpinnings for the spire atop Donald Trump’s Chicago skyscraper, which ranks as America’s second-tallest building after Sears Tower.

Sikorsky S-61 helicopter dangled three-legged steel sections of the spire over the tower’s roof. Ironworkers aligned the sections, then bolted them into place, despite the blasts of cold air from the winds and the helicopter’s clattering blades.

As the spectacle unfolded more than 1,300 feet above the sidewalk, with the chopper levitating near such landmarks as the Wrigley Building, pedestrians on Michigan Avenue stopped in their tracks and recorded the sight with a variety of devices–cell phone cameras, camcorders and conventional cameras.

After the helicopter lowered the fifth section of the spire into place, an iron worker clad in a red jacket climbed to the top of the section and disengaged the cable to which the steel piece had been attached. Seen through binoculars, he resembled a fly. “That’s the lead dog pulling the sled,” said one onlooker on the construction team.