[1] The National Transportation Safety Board (NTSB) concluded that the crash was caused by the captain's improper execution of an instrument approach, combined with a severe downdraft at a low altitude, which resulted in the aircraft descending uncontrollably into terrain.

The northern approach, called "VOR/DME 19", was not legally available to the crew under these circumstances, as Mohawk company policy prohibited reliance on DME as a primary navigational instrument.

Instead, the crew appeared to select an improvised and unauthorized modified version of the VOR/DME 19 approach, which included flying outbound followed by a course reversal at about 10 nautical miles (20 km) north of the airport, over Lake George.

As the crew performed what appeared to be an unpublished and unauthorized procedure turn for course reversal on the VOR/DME 19 approach path, they descended prematurely and hit the side of a mountain.

In their final report, issued on June 25, 1970, the NTSB determined the following official Probable Cause for the accident:[1]The captain, while conducting an approach, exceeded his clearance limits and, thereafter, flew the aircraft into a severe "lee of the mountain downdraft" at an altitude insufficient for recovery.