DEN08FA092

The loss of tail rotor effectiveness and the pilot's failure to regain aircraft control. Contributing to the accident was the pilot's decision to fly in known adverse weather conditions and the gusty winds generated from convective outflow. Contributing to the severity of the injuries was the pilot's failure to provide a safety briefing to his passengers in accordance with Federal Aviation Regulations.

According to the pilot, he was approaching his personal helipad when the helicopter started rotating rapidly to the right. Multiple witnesses reported that the helicopter approached the landing zone from the north and maneuvered to land, at which time the helicopter began spun to the right four or five times before impacting the water. The pilot and three passengers were able to egress from the helicopter. One passenger drowned. No passenger briefing was conducted and none of the occupants were shown how to use their seatbelts or doors as required in 14 Code of Federal Regulations Part 91.107. The victim, who was sharing a seatbelt with another passenger, had never flown in the helicopter before and was unfamiliar with the exits in the helicopter and how to operate them. According to one passenger and multiple witnesses, thunderstorms and lightning were observed at the time of the accident. Extreme weather radar echoes containing thunderstorms were recorded southwest through the east of the accident site. An analysis conducted by Safety Board meteorologists indicates that turbulence, including vertical and horizontal wind changes, would have been associated with this thunderstorm activity. The terrain would have enhanced the intensity of these parameters, resulting in an encounter of a strong convective outflow of approximately 45 knots from the south. Toxicology testing of blood drawn within an hour after the accident detected butalbital (a prescription barbiturate typically used for severe headaches) and diphenhydramine (an over-the-counter antihistamine commonly known by the trade name Benadryl). The drug levels suggest that the butalbital was likely taken more than 24 hours prior to the accident and that the diphenhydramine was likely taken much more recently (probably on the day of the accident). The pilot had a history of diabetes diagnosed in 1993, with no documentation in his Federal Aviation Administration medical records since 1994 regarding treatment or control of the disease. It is possible that the diphenhydramine, the conditions for which the detected medications were used, or complications or side effects from long-standing diabetes may have contributed to the pilot's decision to fly and/or his inability to control the helicopter in the prevailing conditions; however, the investigation could not definitively determine this. An examination of the helicopter's systems and structure revealed no preimpact anomalies.

HISTORY OF FLIGHT On May 25, 2008, at 1921 central daylight time, a McDonnell Douglas Helicopter Company MD 500E/369E, N686F, operated by a commercial pilot, impacted the water while attempting to land at a private helipad at Lake of the Ozarks, Sunrise Beach, Missouri. Visual meteorological conditions prevailed at the time of the accident. The personal flight was being conducted under the provisions of Title 14 Code of Federal Regulations Part 91 without a flight plan. The pilot and two passengers reported no injuries; one passenger sustained serious injuries, and one passenger was fatally injured. The local flight departed at 1917. According to the pilot, the short helicopter ride was planned to fly the neighbor's children, his son, and his son's friend around the lake. The flight departed the pilot's residence, proceeded "across the north ridge of the lake," and then reversed course to proceed back towards the pilot's residence. The pilot reported that during approach for landing he initiated a turn towards the east and within a "few second at an altitude of approximately 35 feet, the helicopter began to spin rapidly to the right." The pilot stated that he "applied full opposite direction anti-torque pedal and a slight reduction in collective." He reported that the rotation "increased and became more violent." The helicopter impacted the water and sank. Prior to the spinning, there were no warning lights or sounds. According to the front seat passenger, the flight was short, approximately five minutes in duration. She had not flown in a helicopter before and commented that the helicopter was "rocking" and did not know if this was normal. Just prior to landing the helicopter was "hovering or sitting still." The helicopter spun around once, paused, spun around again really fast, and eventually impacted the water. The rear seat passenger reported that the "tail" of the helicopter struck the water first. The Missouri State Water Patrol took witness statements from twelve individuals. The National Transportation Safety Board (Safety Board) Investigator in Charge (IIC) interviewed two witnesses and received four additional witness statements. According to these witnesses the helicopter approached the landing zone from the north and made several turns, as if maneuvering to land. The helicopter turned towards the east and slowed to a hover. One witness reported that the helicopter made a "very quick 90-degree turn." The helicopter then rotated around, stopping on an approximate heading of east as it impacted the water. Multiple witnesses reported that the helicopter was spinning around to the right, multiple times, at a very high speed. The helicopter impacted the water and sank very quickly. PERSONNEL INFORMATION The pilot, age 50, held a commercial pilot certificate with airplane single engine land and sea, multi-engine land and sea, rotorcraft helicopter, and instrument airplane ratings. He was issued a second class airman medical certificate on February 7, 2008. The certificate contained the limitation "must have available glasses for near vision." According to the Pilot/Operator Aircraft Accident Report form submitted by the pilot, he had logged approximately 2,360 hours total time; 560 of which were in rotorcraft, and 350 of which were in the make and model of the accident helicopter. He reported that he had logged 33 hours total within the previous 90 days, 10 hours of which were in the make and model of the accident helicopter. His last flight review was successfully completed on February 4, 2008, in the accident helicopter. AIRCRAFT INFORMATION The accident helicopter, a McDonnell Douglas 500E Model 369E (serial number 0524E), was manufactured in 1995. It was registered with the Federal Aviation Administration on a standard airworthiness certificate for normal operations. The helicopter was powered by an Allison 250-C20B (Rolls-Royce) turbo shaft engine rated at 420 horsepower. The helicopter was equipped with a five-blade main rotor system. The helicopter was registered to Impact Aviation LLC, operated by the pilot, and was maintained under an annual inspection program. A review of the maintenance records indicated that the last annual inspection had been completed by A & S Helicopters, Inc, of Cahokia, Illinois, on February 8, 2008, at an airframe total time of 4,345.5 hours. The airplane had flown 10.1 hours between the last inspection and the accident and had a total airframe time of 4,355.6 hours. METEOROLOGICAL INFORMATION Level II Doppler weather radar data for Springfield (KSGF), Missouri, scanned the accident area at 1914:21, 1919:13, and 1924:05. The weather radar beam center was approximately 7,800 feet with the beam width of 6,800 feet. Data indicated reflectivity values of 35 to 60 dBz just south of the accident site. The Range Height Indicator Base Reflectivity Image for 1919:13, for the radial through the accident site, depicted weather radar echo tops of 48,000 feet in the accident area. The National Weather Service Storm Prediction Center in Norman, Oklahoma, issued two severe thunderstorm watches (364 and 366) for areas just north and east of the accident location and a tornado watch for areas just south (358) of the accident location. Watch 364 was issued from 1600 to 2200. Hail, thunderstorm wind gusts to 70 miles per hour, and dangerous lightning were forecasted. Watch 366 was issued from 1835 to 0200 with the same weather expectations. Tornado watch 358 was effective from 1315 to 2000. Tornadoes, hail, thunderstorm wind gusts to 70 miles per hour, and dangerous lightning were forecasted. Convective significant meteorological advisory (SIGMET) 02C was issued at 1755 and was valid until 1955 and covered the accident aircraft route of flight and landing location. The SIGMET advised of an area of severe thunderstorms moving from 270 degrees at 25 knots. Cloud tops were forecast to be above flight level 450. Tornadoes, hail, and wind gusts to 60 knots were possible. The closest official weather observation station was Lee C Fine Memorial Airport (KAIZ), Kaiser Lake Ozark, Missouri, located 7 nautical miles (nm) southeast of the accident site. The elevation of the weather observation station was 869 feet msl. The routine aviation weather report (METAR) for KAIZ, issued at 1915, reported, winds, 160 degrees at nine knots, gusting to 16 knots; visibility, six miles with thunderstorms; sky condition, few clouds at 2,400 feet, scattered clouds at 5,500 feet, broken ceiling at 9,500 feet; temperature 20 degrees Celsius (C); dewpoint, 18 degrees C; altimeter, 29.87 inches. Distant lightning was noted in all quadrants and 0.14 inches of rain was reported. The METAR for KAIZ issued at 1935, reported winds 180 degrees at 22 knots gusts to 47 knots; visibility 1 1/2 miles with thunderstorms; sky condition, scattered clouds at 1,100 feet, broken ceiling at 2,400 feet, overcast at 5,500 feet; temperature 20 degrees C; dew point 17 degrees C; altimeter setting 29.95 inches. Distant lightning was noted in all quadrants and 0.48 inch of rain was reported. According to the pilot, at the time of the accident the sky was clear, there was no turbulence, and he estimated the wind speed at eight knots. He stated he was using smoke in the area and a flag near his residence to determine wind speed and direction. The front seat passenger stated that the sky was dark towards the "house" and she observed lightning in that direction. She reported that the winds were calm, and then they would "pick up." During the flight the pilot commented to her about the "incredible winds." Multiple witnesses to the accident reported strong, gusty surface winds at the time of the accident. There was no evidence located indicating that the pilot obtained a weather briefing from either the Flight Service Station or Direct User Access Terminal Systems (DUATS). The pilot reported on his accident report form that he obta