N629EHSchweizer Aircraft G-164B · 1991

On July 26, 2022, about 1330 central daylight time, a Schweizer Aircraft Corporation G-164B airplane, N629EH, sustained substantial damage when it was involved in an accident near Knox, Indiana. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 137 aerial application flight.

According to the pilot, the accident flight was the 5th aerial application flight of that day. Shortly after takeoff, about 15 ft agl, the airplane would not continue to climb. The pilot stated that he 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 about 300 ft from the end of the grass airstrip. The airplane came to rest in the corn field and sustained substantial damage to the fuselage and wings (see Figure 1).

Figure 1. Accident airplane as it came to rest in a field (Source: Federal Aviation Administration (FAA))

The pilot reported he had exclusively been operating the airplane for about 5 years without experiencing an issue. According to the pilot and airplane records, a 100-hour inspection was completed on July 18, 2022, and an overhauled propeller governor was installed for an unknown reason during that inspection. The airplane had accumulated about 40 hours total time since the 100-hour inspection.

A review of the aircraft records revealed that on May 16, 2013, the Pratt & Whitney PT6A-34 engine was installed on the airplane in accordance with supplemental type certificate (STC) SA1377GL. The airplane flight manual supplement for the engine STC, to include revised performance charts, was not located with the pilot’s operating handbook. On July 8, 2018, the airplane completed a flight check in accordance with the Civil Aeronautic Manual that increased the special purpose loading to 4,200 pounds. According to the FAA, based on the pilot’s reported load weight for the accident flight, the airplane was being operated within the weight limitations of the airplane.

Aircraft recovery personnel reported that when they removed the airframe to engine fuel line, “a lot” of fuel drained from the fuel line. Initial postaccident examination revealed earthen debris within the compressor and power turbine sections. The engine air lines and accessories, to include 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. The blades displayed leading edge damage and chordwise scratching.

Visual examination of the engine revealed external damage consistent with the 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 the top and bottom. The compressor turbine shroud displayed localized scoring wear, consistent with compressor turbine blade impacts. The 1st 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. The blade tips and shroud exhibited rubbing wear. There were no indications of any preimpact mechanical anomalies with the engine that would have precluded normal operation.

Due to damage, the fuel pump and fuel control unit (FCU) were unable to 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 the appearance of 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 for 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 and no leaks were detected. Chemical examination of the black deposits revealed the presence of environmental contaminants and engine oil.

The start flow control unit was partially tested due the improper transfer valve which prevented further testing. The transfer valve was removed and disassembled, which revealed 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 the presence of 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.