19990419044599A

(-23) During takeoff pilot reported hearing several pop sounds coming from engine followed by engine power loss. As a result aircraft collided with electrical wires causing a/c to strike ground causing nose roll-over. No injuries reported. (.4) the pilot said that he had just taken off from a farm airstrip and was initiating a turn to clear a building when several 'pop' sounds came from the engine and it began to lose power. The pilot was unable to clear a set of power lines and struck the wires. Ground witnesses said they watched the aircraft liftoff from the airstrip and begin a gentle left turn to clear a building. In the turn a trail of black smoke began coming from the aircraft as it started a shallow descent toward a field. Just before the aircraft hit the power lines, a large puff of black smoke emanated from the aircraft. After colliding with the wires, the aircraft hit the ground and nosed over. The witnesses heard distinct 'popping sounds' associated with the onset of the smoke trail. The engine was removed and transported to a turbine engine overhaul facility for examination. Teardown of the engine revealed that one blade in the power turbine wheel had failed at the root section and was not recovered. Two other blades were fractured at their approximate midspan point and the outboard blade sections were not recovered. All other blades around the disk exhibited nicks and gouges in the leading edges. All fracture surfaces exhibited granular features. The compressor bleed valve would not hold pressure and was found to be leaking from the seal under the seal support plate-securing nut. Review of the engine maintenance records disclosed that the compressor bleed valve was installed on the engine 605 hours prior to the accident. Prior to installation on the engine, a new diaphragm was installed in the valve.