2005 Eurocopter AS 350 BA accident near Oberwiesenthal

Overview and immediate circumstances On 22 September 2005, a Eurocopter AS 350 BA helicopter crashed in a forested area near Oberwiesenthal, Germany. The aircraft was engaged in a forest liming operation in the Pfahlberg area. The pilot, a 39-year-old flight instructor, was seriously injured, and the helicopter was destroyed. The accident site was located approximately 35 meters west of the loading site, where the helicopter came to rest on the forest floor after striking trees. ## Flight details and pilot background The helicopter took off in a westerly direction with a fully loaded external lime container after a refueling break of about one hour. The pilot reported that the aircraft had reached an obstacle clearance height of approximately 140 feet when a sudden left yaw occurred during a vertical climb. Attempts to counteract the yaw using the tail rotor pedals and reducing engine power were ineffective. The pilot held a commercial pilot license for helicopters, was experienced with the AS 350 type, and had a total flight experience of approximately 7,000 hours, including about 4,000 hours in agricultural flying. ## Aircraft and operational conditions The Eurocopter AS 350 BA, manufactured in 1984, was registered in Germany. The aircraft had a maximum takeoff weight of 2,100 kg and an operating empty weight of 1,158 kg. It was operating at its maximum takeoff weight, with a full fuel tank for the next hour of flight and a fully loaded external lime container. The last maintenance inspection was conducted on 24 May 2005, and the aircraft had a total operating time of 6,192 hours. ## Meteorological and site conditions The weather at the time of the accident was clear with visibility greater than 10 km. A weather station located 2 km away and 200 m higher recorded a wind of 13 kt from the east, with gusts up to 17 kt, and a temperature of 7 °C. The loading site was in hilly terrain, situated on the lee side of a slope in an easterly wind. The site was a clearing in a dense, tall spruce forest, with low vegetation on the approach from the east and high vegetation on the departure to the west. ## Investigation findings The investigation found that the helicopter was operating at its maximum takeoff weight and required a vertical takeoff to clear the surrounding trees. The high engine power required during the takeoff generated a strong counter-torque, which was to be balanced by the tail rotor. The left yaw that occurred was attributed to a “loss of tail rotor effectiveness,” a condition that could be triggered by factors such as low forward speed, high engine power demand, and maximum takeoff weight. The easterly wind above the tree line further negatively affected the directional stability of the helicopter. The pilot, despite his extensive experience, was unable to stop the yaw and lost control of the aircraft, leading to the crash.