HISTORY OF FLIGHTOn June 29, 2014, about 1730 mountain daylight time, an Aerospatiale AS350B2, N350CR, collided with terrain near Dietrich, Idaho. Reeder Flying Service was operating the helicopter under the provisions of 14 Code of Federal Regulations (CFR) Part 135. The commercial pilot and two passengers sustained serious injuries. The helicopter sustained substantial damage during the accident sequence. The cross-country aerial photography flight departed Twin Falls, Idaho, about 1630, with a planned destination of Rexburg, Idaho. Visual meteorological conditions (VMC) prevailed, and no flight plan had been filed. Witnesses reported that the helicopter was traveling in a northeasterly direction when they observed it make a sudden 180-degree reversal to the southwest, followed by a rapid tail-first descent into the ground. The pilot reported that the purpose of the flight was to position the helicopter and its installed camera equipment to a staging area of an intended aerial videography project. One passenger was in the front left seat to operate the camera, and the other was behind the pilot in the right rear outboard seat. According to the pilot, prestart, run-up, and hover checks were uneventful. He flew to a scenic waterfall, and flew two orbits to test the camera equipment and its imaging. He then notified his maintenance department that he was preceding to the staging area. He climbed the helicopter to 800-1,000 ft agl; shortly thereafter the pilot lost consciousness. His next recollection was waking up in an intensive care unit at a hospital. After the pilot lost consciousness, the front seat passenger attempted to control the helicopter using the cyclic; however, the helicopter eventually collided with terrain. PERSONNEL INFORMATIONThe 57-year-old pilot held a commercial pilot certificate with ratings for airplane single-engine land, helicopter, and instrument. The pilot held a flight instructor (CFI) certificate with ratings for helicopter and instrument helicopter. The pilot held a second-class medical certificate issued on March 24, 2014, with no limitations or waivers. The pilot reported that he had a total flight time of 7,405 hours with 2,683 hours in this make and model. He logged 88 hours in the previous 90 days, and 39 in the previous 30 days. He completed a flight review on April 10, 2014. AIRCRAFT INFORMATIONThe helicopter was an Airbus Helicopters, Inc., AS350B2, serial number 2328. The operator reported that the helicopter had a total airframe time of 8,887 hours at the time of the accident. It had a 100-hour inspection on April 11, 2014. The engine was a Honeywell LTS 101-700D-2, serial number LE-46019C. The pilot reported that the total time on the engine was 6,518 hours, and time since major overhaul was 904 hours. AIRPORT INFORMATIONThe helicopter was an Airbus Helicopters, Inc., AS350B2, serial number 2328. The operator reported that the helicopter had a total airframe time of 8,887 hours at the time of the accident. It had a 100-hour inspection on April 11, 2014. The engine was a Honeywell LTS 101-700D-2, serial number LE-46019C. The pilot reported that the total time on the engine was 6,518 hours, and time since major overhaul was 904 hours. MEDICAL AND PATHOLOGICAL INFORMATIONThe National Transportation Safety Board's medical officer reviewed the pilot's airman medical file, personal, and hospital medical records and prepared a factual report that is contained in the public docket for this accident. In summary, the pilot had a history of high blood pressure and high cholesterol. The pilot had gastroenteritis the night prior to the accident, and symptoms had reportedly been resolved following treatment with bismuth subsalicylate. The following morning, he reported that he felt that he was well enough to fly. According to postaccident medical records from the pilot's hospital treatment, the pilot suffered a sudden, temporary loss of consciousness (known as a syncopal episode) while controlling the helicopter. Postaccident medical evaluation led to a diagnosis of sick sinus syndrome, a group of heart rhythm disorders that include slow heart rhythm (bradycardia) or periods when the heart pauses for an excessive interval sometimes accompanied by fatigue, confusion or syncope. The condition was treated with an implanted pacemaker the day following the accident. TESTS AND RESEARCHWreckage Examination Investigators from the NTSB, Airbus Helicopters, and Honeywell examined the wreckage at Air Transport, Phoenix, Arizona, on July 15, 2014. A complete report of the examination is in the public docket for this accident. The examination revealed no anomalies with the airframe or engine. The pilot stated that there were no mechanical malfunctions or failures with the helicopter that would have precluded normal operation. Video Study The passengers were filming the flight. A review of the video indicated that the pilot slumped forward in his seat; his body movements were limp and flaccid. The passenger in the front left seat appeared to reach his right hand in front of the pilot near the area of the cyclic. The passenger in the rear seat appeared to reach forward, and try to pull the pilot's upper torso toward the back of the seat. The helicopter then fell forward into the ground.