Burbank, WA, USA
N106TV
BELL 206B
During an aerial application flight, the single engine helicopter was flying low over an apple orchard when the engine began to lose power. The pilot decreased his airspeed toward zero and performed a hovering autorotation into the orchard. During the landing, the rotor blades impacted the trees, and the tail boom separated from the main fuselage. An examination of the engine revealed that the compressor discharge pressure (PC) air tube, which connected the PC air filter to the power turbine governor was disconnected. The “B” nut that connected the tube to the PC air filter was present on the tube but not threaded onto the PC air filter boss. The threads on both the PC air filter boss and the “B” nut did not exhibit any damage or abnormalities. Review of the maintenance records showed that, about 6 hours before the accident, the turbine assembly and bleed valve had been replaced. Removal and reinstallation of the PC air tube was conducted as part of the documented maintenance. It is likely that maintenance personnel did not properly torque the “B” nut when reinstalling the tube and the loose “B” nut backed off in-flight. According to the engine manufacturer's technical representative, disconnection of the PC air tube during engine operation would result in a loss of engine power.
The pilot stated that as he was flying low over the apple orchard and rolled out of a turn, the engine began to lose power, which was accompanied by the engine out horn and light. He decreased his airspeed towards zero, and performed a hovering autorotation into the orchard. During the landing the rotor blades impacted the trees and the tail boom separated from the main fuselage. An examination of the engine revealed that Pc air tube that connects the Pc air filter to to the Power Turbine Governor (PTG) was disconnected. The b-nut that connects the tube to the Pc air filter was present on the tube but not threaded onto the Pc air filter boss. Review of the maintenance records showed that about 6 hours prior to the accident the turbine assembly and bleed valve had been replaced. The threads on both the Pc air filter and b-nut did not exhibit any damage or abnormalities. The removal and reinstallation of the Pc air tube was conducted as part of the documented maintenance. According to the engine manufacturer's technical representative, the disconnection of the Pc air tube during engine operation would result in a loss of engine power.
The failure of maintenance personnel to properly torque an air tube fitting, which resulted in a total loss of engine power.
Source: NTSB Aviation Accident Database
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