McCormack, 58, was not authorized to fly in limited visibility, according to Federal Aviation Administration records.
The helicopter cut an erratic path over the East River and then Manhattan, changing course and altitude several times during the 10-minute flight, according to the NTSB. Citing preliminary flight tracking data, officials said McCormack flew within 500 feet of the Manhattan heliport before reversing course. Video provided to NTSB by a witness showed the helicopter diving and climbing in and out of the clouds.
The helicopter slammed into the roof of the 54-story AXA Equitable building in midtown Manhattan around 1:40 p.m.
The crash decimated the helicopter, sending small pieces of debris to the street below and sparking a fire.
The preliminary report did not include any conclusions about the cause of the crash, but the details it contained pointed to the strong likelihood that foul weather played a role in the crash. It also raised the possibility that the helicopter was descending rapidly when it hit the roof.
The Associated Press contributed to this report.