N3633B

On April 19, 1999, at 0752 hours Pacific daylight time, a Schweizer G-164B, N3633B, collided with power lines following a power loss during the takeoff initial climb from a private farm airstrip near Marysville, California. The aircraft was owned and operated by Onstott Dusters, Inc., of Yuba City, California, under 14 CFR Part 137 of the Federal Aviation Regulations. Visual meteorological conditions prevailed at the time and no flight plan was filed for the local area aerial application flight. The aircraft sustained substantial damage. The commercial pilot, the sole occupant, was not injured. The flight was originating at the time of the accident and was loaded with 1,800 pounds of fertilizer to be applied to a neighboring field.

In verbal and written statements, the pilot reported that he had just taken off from the airstrip and was initiating a turn to clear a building when several "pop" sounds came from the engine and it began to loose power. The pilot was unable to clear a set of power lines and struck the wires.

A Yuba County road crew was working on a road close to the accident site and witnessed the accident. The workers said they watched the aircraft liftoff from the airstrip and begin a gentle left turn to clear a building. In the turn, the workers saw a trail of black smoke begin coming from the aircraft as it started a shallow descent toward a field, which is across the road. 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 said they heard distinct "popping" sounds associated with the onset of the smoke trail.

The power lines contacted by the aircraft were strung between telephone-type poles and were about 25 feet above the ground.

Following recovery of the airplane from the site, the engine was removed and transported to a turbine engine overhaul facility for examination under the supervision of an Federal Aviation Administration Airworthiness Inspector from the Sacramento, California, Flight Standards District Office. 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 was installed in a calibrated test bench for a functional test. The unit would not hold pressure and was found to be leaking from the seal under the seal support plate-securing nut. The fuel control unit and engine driven fuel pump functioned to specification.

Review of the engine maintenance records disclosed that the compressor bleed valve was installed on the engine on March 9, 1998, 605 hours prior to the accident. Prior to installation on the engine, a new diaphragm was installed in the valve.