What happened
On May 25, 2008, a McDonnell Douglas MD 500E helicopter, registration N686F, crashed into the water at Lake of the Ozarks near Sunrise Beach, Missouri. The flight, which was being conducted under Part 91 regulations without a flight plan, was a short local trip intended to fly family and friends around the lake.
As the pilot approached a private helipad, he initiated a turn to the east. At an altitude of approximately 35 feet, the helicopter began to spin rapidly to the right. The pilot attempted to correct the rotation by applying full opposite anti-torque pedal and reducing the collective, but the rotation became more violent. The aircraft impacted the water and sank.
One passenger sustained fatal injuries, while the pilot and two other passengers sustained serious and minor injuries. Witnesses reported seeing the helicopter perform several high-speed right-hand rotations before hitting the water.
The investigation
Investigators examined the wreckage, which was recovered from 35 to 40 feet of water. While the fuselage and engine were recovered, the five main rotor blades were not found. The investigation of the tail rotor drive shaft revealed a separation point characterized by twisting and collapsing, with findings consistent with torsional overstress.
Meteorological analysis showed that the area was experiencing thunderstorm activity. While the pilot reported calm winds, radar and local observations indicated the presence of a strong convective outflow of approximately 45 knots from the south, which likely introduced significant turbulence and wind changes.
Toxicology testing of the pilot's blood revealed the presence of diphenhydramine and butalbital. Additionally, investigators reviewed the pilot's medical history, noting a diagnosis of diabetes from 1993 that was not documented in more recent FAA medical records.