On May 12, 1998, about 1900 central daylight time, an unregistered two-place ultralight, an M2 Sport 1000, owned and operated by a private individual as a 14 CFR Part 91 personal flight, crashed during initial climbout from a private grass strip near Semmes, Alabama. Visual meteorological conditions prevailed and no flight plan was filed. Two unrated occupants sustained fatal injuries, and the aircraft was destroyed. The flight was originating at the time of the accident. The craft was being flown without an FAA waiver for two-occupant flight. Reports indicated that localized turbulence existed somewhere off the departure end of the strip, and immediately after the craft flew into that area, at 200 to 300 feet agl, it was observed to abruptly reverse course and descend toward its departure point. The craft impacted a 6 to 8 foot embankment within a dirt pit about 100 yards short of the grass strip. According to a statement by one of the local ultralight operators present at the strip, he flew with the accident-operator just previous to the accident flight and they encountered the same turbulence. At the point they entered the "choppy" air, the accident-operator reduced power and his passenger/dual-operator remembered thinking at the time that reducing power was the wrong corrective action. A third ultralight operator who took off immediately prior to the accident flight also encountered the turbulence, and stated he needed full power and full aileron deflection to counter the forces. When he quickly determined that wasn't enough, he used full rudder deflection. Once out of the turbulence, looking back to his departure point, he observed the accident craft as it entered the turbulence, saw the right wing "kick up" to about the vertical position, saw the craft enter a 180 degree left turn and descent back toward the strip, and then saw the collision with the dirt embankment. Examination of the wreckage by Mobile County Sheriff's Department personnel revealed that the ultralight impacted the embankment in an upright, nose-down attitude with the nose-wheel and dual rudder pedal assembly absorbing much of the energy. No evidence of precrash defects were noted for airframe structural integrity or flight control path integrity; however, proper control deflection could not be determined because of the damage. The Rotax 618 engine had torn loose from the airframe due to impact. The engine was shipped to South Mississippi Light Aircraft, Inc., and with FAA oversight, test-run on July 2, 1998. Except for those components that received impact damage or misalignment and had to be reinstalled, the engine was cranked, as is, and started immediately. It was accelerated through its full operating range with satisfactory results. The magnetos were checked, satisfactorily. See FAA Inspector's report and "Record of phone conversation." Postmortem examination of both occupants was performed by Julia C. Goodwin, M.D., State Medical Examiner, Alabama Department of Forensic Sciences, Mobile, Alabama. The cause of death for both occupants was reported as multiple blunt force injuries. No findings that could be considered causal to the accident were reported. Postmortem toxicology studies on specimens obtained from the occupants were performed by Dennis V. Canfield, Ph.D., Manager, FAA Toxicology and Accident Research Laboratory, Oklahoma City, Oklahoma, as well as the Alabama State Medical Examiner, Dr. Julia C. Goodwin. The tests were negative for carbon monoxide, cyanide, ethanol, basic, acidic, and neutral drugs for the left seat occupant. For the right seat occupant, the tests were negative for carbon monoxide, cyanide, and ethanol, but positive for marihuana and chlorpheniramine, an antihistamine.