Lt. Col. Morris Fontenot Jr., a member of the Massachusetts Air National Guard, was killed in the August crash near Deerfield.
Air Combat Command released its crash investigation report Monday.
The investigation says Fontenot was incapacitated during a rapid descent, rendering him unable to recover or eject from the aircraft. The Air Force says the investigation board didn't have enough evidence to pinpoint why Fontenot was incapacitated.
At the time of the crash, Fontenot was flying from Barnes Air National Guard Base in Massachusetts to Naval Air Station Joint Reserve Base New Orleans so the aircraft could receive a radar upgrade.