ERA15LA376

The commercial pilot was flying the helicopter about 600 ft above ground level and at a speed of 60 to 70 mph and began descending and slowing the helicopter as it approached a friend's home, where he planned to land. The right-seat passenger, who was a student pilot, reported that the helicopter got "low and slow" during the approach and began "violently spinning to the right." The student pilot also reported that the wind was light and variable and that there were no mechanical malfunctions or failures during the flight. Postaccident examination of the wreckage revealed no evidence of a mechanical malfunction or anomaly. A cell phone video provided by a witness confirmed the student's report that the helicopter was at a low altitude and airspeed when it yawed right, then spun right, and descended to ground impact. The engine could be heard running throughout the accident sequence. It is likely that, during the landing approach, the helicopter's airspeed dropped below effective translational lift, and when the pilot added power to compensate, the helicopter yawed right. The pilot was unable to stop the yaw and lost control of the helicopter due to a loss of tail rotor effectiveness.

On September 25, 2015, about 1040 eastern daylight time, a Hughes 269B, 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 the provisions of 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 (LEE) about 1020. The student pilot reported the following. He was in the right, cockpit seat and the pilot was in the left seat. The pilot was approaching the residence of a friend, at an altitude of 600 feet above the ground and a speed of 60-70 mph. The pilot began descending and slowing down the helicopter as they approached the residence. The helicopter then began "spinning slowly to the left a few times then violently spinning to the right." He then recalled waking up on a medical air ambulance helicopter after the accident. The student pilot later reported that the helicopter was "low and slow" during the approach and that there was no mechanical malfunction or failure during the accident flight. He reported the wind as light and variable. He also stated that the height-velocity curve for the Hughes 269B should have been followed. An inspector with the Federal Aviation Administration (FAA) responded to the accident site and examined the wreckage. The helicopter came to rest on its right side. The main rotor blades received 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 there was oil in the engine. An external examination of the engine revealed no anomalies. His overall assessment of the wreckage did not reveal any evidence of a mechanical malfunction or anomaly. The cellular telephone video provided by a witness confirmed the left hand and right hand yaw and spiral during the final descent. The engine could be heard running throughout the accident sequence. The FAA issued Advisory Circular (AC) 90-95, Unanticipated Right Yaw in Helicopters, in February 1995. The AC stated that the loss of tail rotor effectiveness (LTE) was a critical, low-speed aerodynamic flight characteristic which could result in an uncommanded rapid yaw rate which does not subside of its own accord and, if not corrected, could result in the loss of aircraft control. It also stated, "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 covered conditions under whichLTE may occur. It stated: "Any maneuver which requires the pilot to operate in a high-power, low-airspeed environment with a left crosswind or tailwind creates an environment where unanticipated right yaw may occur." Paragraph 8 of the AC stated: "OTHER FACTORS...Low Indicated Airspeed. At airspeeds below translational lift, the tail rotor is required to produce nearly 100 percent of the directional control. If the required amount of tail rotor thrust is not available for any reason, the aircraft will yaw to the right." Paragraph 9 of the AC stated: "When maneuvering between hover and 30 knots: (1) Avoid tailwinds. If loss of translational lift occurs, it will result in an increased high power demand and an additional anti-torque requirement. (2) Avoid out of ground effect (OGE) hover and high power demand situations, such as low-speed downwind turns. (3) Be especially aware of wind direction and velocity when hovering in winds of about 8-12 knots (especially OGE). There are no strong indicators to the pilot of a reduction of translation lift... (6) Stay vigilant to power and wind conditions."