Ft. Pierce, FL, USA
N911SL
BELL OH-58A
The pilot was maneuvering the helicopter at low altitude during a search mission. After completing a low level, slow speed, right turn, the helicopter experienced a nose dip and began to spin. The pilot took corrective actions in an attempt to stop the spinning, but the actions failed, and the helicopter impacted the ground hard. No preimpact mechanical irregularities were noted with the helicopter during the wreckage examination. The pilot stated that he was more focused on the mission than on flying the helicopter and was caught off guard when the uncommanded right yaw started. He reported that he lost awareness of the wind condition and did not recognize the possibility of a loss of tail rotor effectiveness (LTE) event. As a result of the accident, the helicopter operator implemented additional training and awareness courses and required their pilots to complete mission-oriented emergency procedures flight training and specific training on LTE prevention, onset, and recovery.
HISTORY OF FLIGHT On May 29, 2011, about 1248 eastern daylight time, a Bell helicopter, OH-58A, N911SL, registered to and operated by the St. Lucie County Sheriff’s Office, collided with the ground while maneuvering near Fort Pierce, Florida. The certificated airline transport pilot received minor injuries and the helicopter incurred substantial damage. Visual meteorological conditions prevailed for the local flight, and a company flight plan was filed. The flight originated from the St. Lucie County International (FPR), Fort Pierce, Florida, about 1232, The helicopter was called to assist in a search for a possible ejected passenger from a vehicle involved in a rollover accident. A witness stated to the responding Federal Aviation Administration (FAA) inspector that the helicopter was about 300 feet above ground level (agl) when it climbed in a southeast direction to about 400 feet agl. As the helicopter was heading back to the north- northwest, it began to spin and the nose oscillated up and down. It continued to spin and finally dropped on its skids in the grass median between the highway and the on ramp. The helicopter incurred substantial damage to its underside, skids, and tail boom, which separated before the helicopter came to a complete stop. The pilot stated he was heading west with a tailwind, as he started a right turn back to the north, and did not recognize the possibility for a LTE (loss of tail-rotor effectiveness) situation. As the helicopter reached a northerly heading, the nose dipped and an uncommanded right yaw began. The pilot applied left pedal, forward cyclic, and pushed the collective down to stop the rotation. The rotation did not stop and as the helicopter got close to the ground, he rolled the throttle off to slow rotation and pulled up on the collective. The helicopter impacted the ground hard, in an uncontrolled descent. PERSONNEL INFORMATION The pilot held an airline transport pilot certificate and commercial pilot certificate with ratings for airplane single and multiengine land, helicopter, and an instrument rating for airplane and helicopter. He also held a certified flight instructor certificate with ratings for airplane single and multiengine land, helicopter, and instrument airplane. He was issued an FAA second-class medical certificate on August, 18, 2010 with limitations. At that time, he reported a total of 6,150 flight hours. He reported a total of 679 hours in make and model of the accident helicopter. METEOROLOGICAL INFORMATION The closest official weather observation was at FPR, 5 miles north of the accident site. The JKL 1253 METAR, was winds 080 at 10 knots (kt), gusting 18 kt; visibility 10 statute miles; scattered clouds at 3,000 above ground level, temperature 29 degrees Celsius (C); dew point 19 degrees C; altimeter 30.06 inches of mercury. WRECKAGE AND IMPACT INFORMATION A postaccident examination of the helicopter by an FAA inspector revealed the skids were separated from the airframe and the tail rotor section was separated from the tail boom, which was bent upward just aft of the cabin area. The front windshield was broken and the lower forward and aft section of the fuselage incurred impact damage. The engine, main transmission, and tail rotor gearbox all rotated freely; and their respective chip detectors and oil filters revealed no evidence of ferromagnetic particles. Continuity of all flight controls was also verified. No preimpact mechanical irregularities were noted during the examination. ADDITIONAL INFORMATION FAA Guidance Federal Aviation Administration Advisory Circulars (AC) 90-95, Unanticipated Right Yaw in Helicopters, makes reference to loss of tail rotor effectiveness (LTE). LTE is a critical; low-speed aerodynamic flight characteristic which can result in an uncommanded rapid yaw rate which does not subside of its own accord and, if not corrected, can result in the loss of aircraft control. There is greater susceptibility for LTE in right turns. This is especially true during flight at low airspeed since the pilot may not be able to stop rotation. The helicopter will attempt to yaw to the right. Correct and timely pilot response to an uncommanded right yaw is critical. The yaw is usually correctable if additional left pedal is applied immediately. If the response is incorrect or slow, the yaw rate may rapidly increase to a point where recovery is not possible. The pilot must anticipate these variations, concentrate on flying the helicopter, and not allow a yaw rate to build. Caution should be exercised when executing right turns under conditions conducive to LTE. It has been determined to be a contributing factor in a number of accidents in various models of U.S. military helicopters and in several civil helicopter accidents wherein the pilot lost control. In most cases, inappropriate or late corrective action may have resulted in the development of uncontrollable yaw. These mishaps have occurred in the low-altitude, low-airspeed flight regime while maneuvering, on final approach to a landing, or during nap-of-the-earth tactical terrain flying. Typical civil operations include powerline patrol, electromagnetic survey, agricultural spraying, livestock herding, police/radio traffic watch, emergency medical service/rescue, and movie or television support flights. Safety Changes As a result of the accident, the operator implemented several awareness courses as part of their training and daily operational protocols. These courses included: Crew Resource Management for single pilot decision making, emotional reactivity, mission call stressors awareness, and continuous awareness training regarding the OH-58 flight dangers and limitations. All of the operator’s pilots to attend courses on mission-oriented emergency procedures flight training and specific flight training on LTE (prevention, onset, recovery).
The pilot's failure to recognize and avoid a loss of tail rotor effectiveness, which resulted in a loss of control and hard landing.
Source: NTSB Aviation Accident Database
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