FTW97LA223

Shortly after takeoff, the agricultural airplane lost power. During the forced landing, the airplane was destroyed. Wreckage examination revealed that the propeller blades were in the flat pitch range, bent straight rearward. The blades did not have a twist set nor was there leading edge damage corresponding to powered rotation at impact. Engine examination revealed that all of the blades of the compressor turbine disc were damaged or fragmented. Two of the 58 blades were found fractured at the root and several blade tips showed thermal distress. The compressor disc shroud segment had ballistic indentations corresponding to the fragmented compressor blades. Both power turbine and compressor turbine shroud segments did not show circumferential machining. The fuel filter from the high pressure fuel pump had black residues embedded throughout the filter element. All 58 blades on the compressor turbine disc had been replaced in 1991. No reference was found as to whether or not the replacement blades were new or used parts. The last recorded hot section was in December, 1994, at 7,063.2 hours TSOH. The TSOH at the time of the accident was 7,632.5 hours.

On June 13, 1997, approximately 1600 central daylight time, an Air Tractor AT-400A agricultural airplane, N3161J, owned and operated by East Arkansas Flying Service of West Memphis, Arkansas, was destroyed during a forced landing following a loss of power near Black Oak, Arkansas. The pilot, sole occupant, received minor injuries. Visual meteorological conditions prevailed and no flight plan was filed for the Title 14 CFR Part 137 aerial application flight.

In a telephone interview with the NTSB investigator-in-charge (IIC), the operator stated that shortly after takeoff from a private agricultural airstrip, the engine "completely" lost power. Subsequently, the pilot was forced to "glide" the aircraft into a corn field. Upon impacting the ground, the airplane was destroyed. The pilot, who did not respond to repeated calls by the NTSB IIC, was interviewed briefly by a FAA inspector who responded to the accident scene. The pilot reported that, about 10 seconds after takeoff, the engine "exploded." He further stated that, due to the layout of the airstrip and obstacles, he had executed a down wind takeoff. On scene examination of the wreckage revealed that the propeller blades were in the flat pitch range, bent straight rearward around the engine cowling. The blades did not have a twist set nor was there leading edge damage corresponding to powered rotation at impact.

A teardown of the engine, which was supervised by the FAA inspector, revealed that all of the blades of the compressor turbine disc assembly were damaged or fragmented. Two of the 58 blades were found fractured at the root and several blade tips showed evidence of thermal distress. The compressor disc shroud showed evidence of ballistic indentations corresponding to the fragmented compressor blades. Blades from the power turbine disc assembly were also found fractured. Both power turbine and compressor turbine shroud segments did not show circumferential machining. Additionally, it was noted that the fuel filter from the high pressure fuel pump had black residues embedded throughout the filter element.

A review of the engine maintenance records revealed that all 58 blades on the compressor turbine disc had been replaced on July 22, 1991, with Pratt & Whitney parts. There was no annotation in the records that referenced whether or not the replacement blades were new or used parts. The last recorded hot section was noted in the records as being accomplished on December 12, 1994, at 7,063.2 hours time since overhaul (TSOH). During an annual inspection, performed on February 15, 1996, a "zero" time Hobbs meter was installed. The Hobbs meter reading recorded at the accident scene was 243.4 hours. As of the last recorded annual inspection, performed on April 12, 1997, the engine had 7,632.5 hours TSOH. The engine's TSOH at the time of the accident was 7,632.5 hours.

The compressor turbine disc, the power turbine disc, and the high pressure fuel pump fuel filter element are in the custody of the owner for further metallurgical and material testing to attempt to determine the mode of failure. This office will be informed of the results of that testing and the information, if applicable, will be added to this report.