One frigid morning last month, April Turner sidled up to the parapet of a 21-story apartment building on the Upper West Side, climbed over the edge and dangled herself 188 feet above the pavement.

Suspended by ropes like the ones used by rock climbers, she slid past balcony ledges and window frames, careful not to lock eyes with dumbstruck residents. With a tiny mallet and a point-and-shoot camera, she cataloged cracks and blemishes on the building’s facade, pausing at each floor to feel around for fatal flaws.

If pedestrians bothered to watch, they might have applauded as she touched down near a neighboring nail salon. Without fanfare, she detached her gear, walked back inside the co-op and took the elevator to the roof for another drop — to canvass another section of the postwar building’s dappled face.

It’s all in a day’s work for a growing number of New York City’s building facade inspectors.

The city requires that of the approximately 1 million buildings in New York City, those taller than six stories — more than 14,500 structures — have their facades inspected every five years, to ensure the safety of passers-by below. Rather than using bulky swing-stage scaffolds, like the ones for window washing, or hydraulic cranes that block traffic, an increasing number of design and engineering firms are training their staff to rappel down the side of skyscrapers in search of dangerous defects.