Accident Details
On July 27, 2019, at approximately 2215 Pacific daylight time, a McDonnell Douglas 369E helicopter, registration N438RC, was involved in an accident near Eugene, Oregon. The helicopter was substantially damaged, and both commercial pilots on board were seriously injured. The flight was conducted as a positioning flight under Title 14 Code of Federal Regulations Part 91.
Pilot Report
According to the pilots, they were approaching the airport ramp area for landing from the east. The wind was from the north at 10 knots. When the helicopter was about 25 to 30 feet above the ramp at an airspeed of approximately 25 knots, the left seat pilot reduced left pedal pressure to turn the helicopter to the right into the wind. The pilot then increased left pedal pressure to stop the turn; however, the helicopter continued turning right and began to spin. The pilot lowered the collective, and the right seat pilot took the flight controls in an attempt to slow the spin. The helicopter subsequently impacted the ground hard, spreading the landing skids and resulting in tail rotor contact with the ramp.
Examination Findings
A postaccident examination of the airframe and engine revealed no anomalies that would have precluded normal operation. The helicopter was mostly intact, and control continuity was established throughout with no anomalies noted. Examination of the powertrain identified a fracture of the main driveshaft flexible joint and a fracture of the tail rotor driveshaft. All fracture features displayed signatures consistent with overstress.
Regulatory Guidance
Federal Aviation Administration Advisory Circular (AC) 90-95, "Unanticipated Right Yaw in Helicopters," describes loss of tail rotor effectiveness (LTE) as a critical, low-speed aerodynamic flight characteristic that can result in an uncommanded rapid yaw rate. The AC notes that such a yaw rate does not subside on its own and, if not corrected, can lead to loss of aircraft control. It further lists conditions under which LTE may occur, including any maneuver requiring high power and low airspeed with a left crosswind or tailwind, and notes greater susceptibility for LTE in right turns, especially during low airspeed flight when the pilot may not be able to stop the rotation.