On March 24, 2015, about 1730 eastern daylight time, a Bell 206B, N43CM, was substantially damaged during an autorotation near Taylors Island, Maryland. The commercial pilot and one passenger were not injured. Visual meteorological conditions prevailed and no flight plan was filed. The helicopter was registered to and operated by DC Helicopters Incorporated as a personal flight, which was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. The flight originated from Monmouth Executive Airport (BLM), Farmingdale, New Jersey, about 1530.The pilot reported that the helicopter was in cruise flight at 3,000 feet above ground level, when there was a sudden drop in altitude followed by a 90 degree rotation to the left and a loud "bang." The pilot lowered the collective and noted that the torque gauge went below 10 percent. He then rolled the throttle to idle, entered an autorotation and landed on a shore. Postaccident examination of the helicopter by a Federal Aviation Administration (FAA) inspector revealed that the helicopter's tailboom was buckled near the tail rotor gear box. Further examination revealed that the tail rotor drive shaft was broken. Flight control continuity was confirmed by hand movement of the controls. The cyclic exhibited free movement in all quadrants and the collective exhibited free up and down movement. Corresponding control movement was observed up to the main rotor hub assembly. The tail rotor pedals were moved and control movement was seen at the tail rotor. Drive continuity was established through the drive system with movement observed to the main mast and to the tail rotor drive system. The tail rotor driveshaft on the tailboom exhibited a torsional crack. The tailboom exhibited evidence of tail rotor blade strikes. Both fuel boost pumps were shown to operate when the battery was turned on. The airframe fuel filter was removed and found to be filled with clear and clean fuel and the filter was also clean. The fuel valve was in the off position and motored on when the battery and fuel valve were switched on. The boost pumps were then energized and a steady flow of fuel was present out the "IN" line to the airframe fuel filter. During a postaccident examination of the engine all B-nuts and fittings were checked by hand for torque, and none were loose. The bleed valve was checked by hand for proper operation. The valve operated smoothly with no lateral play of the poppet valve. The engine mounts were intact with no apparent deformities. The engine exhibited no evidence of having been damaged during the accident sequence. The engine cowlings were removed to facilitate examination of the compressor inlet. Examination of the compressor revealed no evidence of compressor damage or failure. Both the N1 (compressor) and N2 (power turbine) rotor systems were rotated by hand. The N1 rotated smoothly with no unusual noise or resistance. Continuity from the compressor through the auxiliary gearbox to the starter/generator was confirmed. Rotation of the N2 confirmed continuity to both the main rotor and tail rotor drives. The engine was removed to be run in a test cell in an attempt to replicate the reported loss of power. A pre-run examination of the engine found no anomalies with the engine, or any damage which might preclude running the engine on a test cell. The engine was installed on a test cell, started, ran normally and met all serviceable engine standards. The engine produced normal power and responded properly to all power demands, including wave-off and sudden throttle and load changes. After the engine test run, the owner of the helicopter sent the engine's fuel control unit (FCU) out for testing. During testing it was noted that one of the technicians found a "slight bend" in the FCU bellow's assembly. The condition of the bellows did not warrant rejection, and the FCU was reassembled and tested in accordance with manufacturer's specifications. During the test it was noted that the FCU performed erratically on the test stand, and failed to meet serviceable standards. The bellows assembly was replaced with an overhauled bellows assembly, and the FCU performed satisfactorily. The subject bellows assembly was then installed on a serviceable FCU, tested, and failed to pass serviceable standards.