The flight was in level cruise flight at FL430. There was significant level 6 thunderstorm activity in the immediate vicinity of the Tulsa VOR at the time of the accident, and SIGMETs had been issued to and received by the flight crew advising of this activity. The flight crew stated that the only weather being depicted by their onboard weather radar was 40 miles from their position at the time of the accident and not in their flight path. According to transcripts of their conversation with air traffic control personnel, approximately five miles west of the Tulsa VOR and two minutes prior to the accident, the flight crew requested and received permission to deviate from the assigned course in order to avoid buildups in their flight path. The flight encountered severe turbulence for a period of about 10 to 20 seconds. The aircraft descended 3,500 feet before the flight crew was able to regain control of the aircraft's descent. The flight then diverted to Memphis, Tennessee in order to obtain medical attention for those persons injured in the cabin section of the aircraft.