NTSB Identification: NYC08FA071
14 CFR Part 91: General Aviation
Accident occurred Sunday, December 30, 2007 in Cherokee, AL
Probable Cause Approval Date: 01/15/2009
Aircraft: BELL 206L-3, registration: N109AE
Injuries: 3 Fatal.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
The helicopter was maintaining a searchlight on a lost hunter as ground personnel attempted to execute a rescue. During the maneuver, the pilot was flying in an out-of-ground-effect hover, or very slow flight below effective translational lift, about 100 to 150 feet above the trees. The maneuver was contrary to the operations manual, which required a minimum altitude of 500 feet above ground level for night searches. It was also contrary to the operations manual as the maneuver fell inside the height-velocity diagram curve, published in the make and model rotorcraft flight manual (RFM). In addition, a company flight data analyst in the communications center was attempting to persuade the pilot to terminate the search due to safety concerns as the helicopter was flying low and slow. The helicopter began to spin right and descend into trees, consistent with loss of tail rotor effectiveness (LTE). During the spin, witnesses reported an engine noise increase and "fireball" coming from the exhaust, most likely as a result of an over-speed/over-temperature condition as the pilot increased engine power attempting to recover from the spin. Review of the RFM did not reveal any information on LTE; however, the operator maintained an LTE training program, which the pilot had completed. Additionally, the Federal Aviation Administration had previously published Advisory Circular (AC) 90-95, which stated that 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. The AC further stated that flight operations at low altitude and low airspeed are particularly susceptible to LTE, with greater susceptibility in right turns. Examination of the wreckage did not reveal any pre-impact mechanical malfunctions.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The pilot's failure to maintain control of the helicopter during an out-of-ground-effect hover. Contributing to the accident was a loss of tail rotor effectiveness. Full narrative available
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