Accident Overview
On September 25, 2015, about 1040 eastern daylight time, a Hughes 269B, registration N9567F, collided with terrain following a loss of helicopter control during an approach to a private landing area near Eustis, Florida. The commercial pilot and a passenger, who was also a student pilot, were seriously injured, and the helicopter was substantially damaged. The helicopter was owned and operated by the student pilot under Title 14 Code of Federal Regulations Part 91 as a personal flight. Day visual meteorological conditions prevailed, and no flight plan was filed. The local flight originated from Leesburg, Florida, about 1020.
Witness and Pilot Accounts
The student pilot reported that he was in the right cockpit seat and the pilot was in the left seat. The pilot was approaching a friend's residence at an altitude of 600 feet above ground level and a speed of 60-70 mph. As the pilot began descending and slowing down, the helicopter began "spinning slowly to the left a few times then violently spinning to the right." The student pilot recalled waking up on a medical air ambulance helicopter after the accident. He later stated that the helicopter was "low and slow" during the approach and that there was no mechanical malfunction or failure during the accident flight. He described the wind as light and variable and noted that the height-velocity curve for the Hughes 269B should have been followed. A cellular telephone video provided by a witness confirmed the left and right yaw and spiral during the final descent, and the engine could be heard running throughout the accident sequence.
Wreckage Examination
An inspector with the Federal Aviation Administration (FAA) examined the wreckage. The helicopter came to rest on its right side. The main rotor blades sustained structural damage and remained attached to their hub. The tail rotor drive shaft was sheared in two locations. The tail rotor blades remained attached to their hub. Control continuity was established from the cockpit to the main rotor and tail rotor system, except for impact damage. There was sufficient fuel on board and oil in the engine. An external examination of the engine revealed no anomalies. The inspector's overall assessment did not reveal any evidence of a mechanical malfunction or anomaly.
Advisory Circular References
The FAA issued Advisory Circular (AC) 90-95, "Unanticipated Right Yaw in Helicopters," in February 1995. According to the AC, loss of tail rotor effectiveness (LTE) is a critical low-speed aerodynamic flight characteristic that can result in an uncommanded rapid yaw rate, which does not subside on its own and, if not corrected, could result in the loss of aircraft control. LTE is not related to a maintenance malfunction and may occur in varying degrees in all single main rotor helicopters at airspeeds less than 30 knots. Paragraph 6 of the AC states that any maneuver requiring high power and low airspeed with a left crosswind or tailwind creates an environment where unanticipated right yaw may occur. Paragraph 8 notes that at airspeeds below translational lift, the tail rotor must produce nearly 100 percent of directional control, and if required thrust is not available, the aircraft will yaw to the right. Paragraph 9 advises avoiding tailwinds when maneuvering between hover and 30 knots, avoiding out-of-ground-effect (OGE) hover and high-power demand situations, being aware of wind direction and velocity in winds of about 8-12 knots (especially OGE), and staying vigilant to power and wind conditions.