A rigging failure caused the air conditioning unit being lifted into place at 261 Madison Ave. in Manhattan to fall to the street 28 stories below on May 31, according to an investigator on the scene.

The massive unit hit the step-backed building as it fell, raining debris on Madison Ave. between 38th and 39th streets and injuring eight people in the area and two construction workers.

There were some reports that the unit fell as it was being put into place or that the floor cracked or gave way as the unit was being moved into place. “None of those are true,” said the investigator, who spoke on the condition of anonymity.

The floors are solid concrete, and there are no cracks in the floor, the investigator said.

The roughly 10-ton air conditioner was being lifted by a 375 ft. Bay Crane being operated by Skylift Contractor Corp. of Brooklyn, N.Y.

Investigators are looking at rigging issues. Preliminary indications are that human error was not involved in the accident.

The New York Dept. of Buildings is investigating the accident.

New York City Buildings Commissioner Rick D. Chandler, speaking at a press conference shortly after the incident, said the crane was in good shape and that the site has had active construction permits since February.