Accident Overview
On July 26, 2022, about 1330 central daylight time, a Schweizer Aircraft Corporation G-164B airplane, registration N629EH, sustained substantial damage during an accident near Knox, Indiana. The aircraft was operating as a Title 14 Code of Federal Regulations Part 137 aerial application flight. The pilot was not injured.
Pilot Report
According to the pilot, the accident flight was the fifth aerial application flight of that day. Shortly after takeoff, at about 15 ft above ground level, the airplane would not continue to climb. The pilot advanced the throttle, but the engine did not seem to respond. The airplane was in a nose-high attitude when the right wing impacted a corn field approximately 300 ft from the end of the grass airstrip. The airplane came to rest in the corn field, sustaining substantial damage to the fuselage and wings.
Aircraft and Maintenance History
The pilot reported he had exclusively operated the airplane for about five years without any prior issues. According to the pilot and aircraft records, a 100-hour inspection was completed on July 18, 2022, during which an overhauled propeller governor was installed for an unknown reason. The airplane had accumulated about 40 hours total time since that inspection.
A review of aircraft records revealed that on May 16, 2013, a Pratt & Whitney PT6A-34 engine was installed in accordance with supplemental type certificate (STC) SA1377GL. The airplane flight manual supplement for the engine STC, including revised performance charts, was not located with the pilot’s operating handbook. On July 8, 2018, the airplane completed a flight check that increased the special purpose loading to 4,200 lb. According to the Federal Aviation Administration (FAA), the airplane was operated within weight limitations based on the pilot’s reported load weight for the accident flight.
Postaccident Examination
Aircraft recovery personnel reported that when they removed the airframe-to-engine fuel line, “a lot” of fuel drained from it. Initial examination revealed earthen debris within the compressor and power turbine sections. The engine air lines and accessories, including the fuel control unit, fuel pump, start control unit, propeller, and overspeed governors, were removed for further examination and testing. All observed fuel and oil filter screens were clear of contaminants. The three propeller blades were bent aft and found loose in the propeller hub, with leading edge damage and chordwise scratching.
Visual examination of the engine showed external damage consistent with impact, and the engine was covered with earthen debris. The compressor and accessory gearbox rotated freely through the starter pad gearshaft splines. The propeller shaft would not rotate; the reduction gearbox was dirty, and the exhaust duct showed torsional buckling at top and bottom. The compressor turbine shroud displayed localized scoring wear consistent with compressor turbine blade impacts. The first stage compressor rotor airfoils contained debris, and the bearings rotated freely. The power turbine vane airfoils contained whitish deposits and debris. The power turbine disc and blades exhibited circumferential scoring wear from contact with the power turbine baffle. Blade tips and shroud showed rubbing wear. There were no indications of any preimpact mechanical anomalies with the engine that would have precluded normal operation.
Fuel System and Accessories
Due to damage, the fuel pump and fuel control unit (FCU) could not be functionally tested and were disassembled. Disassembly of the fuel pump revealed unknown black deposits or contamination on the inside diameter of the FCU front side carbon seal, and the mating surface of the drive gear face showed light circular scratches.
Disassembly of the FCU revealed a material consistent with RTV silicone sealant on the nylon coupling between the fuel pump and FCU. The coupling was removed with unusual resistance, and the driveshaft rotated with resistance. The engine maintenance manual does not allow that type of material to be used to fit the coupling on the driveshaft. Black granular deposits were present in the P3 and Py ports. The FCU governor bellows was tested with no leaks detected. Chemical examination of the black deposits indicated the presence of environmental contaminants and engine oil.
The start flow control unit was partially tested due to an improper transfer valve that prevented further testing. The transfer valve was removed and disassembled, revealing a seized plunger. The plunger showed score marks and contamination on the sleeve bore. Orange colored debris was noted in the minimum pressurizing valve, and contamination was observed in the housing bypass cavity. Chemical analysis of the contaminants revealed iron oxide, silicon dioxide, and other environmental elements.
The propeller and overspeed governors were examined and functionally tested with no anomalies noted. There were no indications of any preimpact mechanical anomalies with the accessories that would have precluded normal operation.