ERA23FA382

A witness reported that the pilot/owner of the experimental amateur-built airplane had recently replaced the aircraft’s propeller and had removed the engine to install a new propeller governor. He indicated that, following the completion of maintenance, the pilot informed him that he intended to fly over the witnesses’ property and perform a flyby. After performing a low pass over the witness’s field, the pilot initiated a climbing left turn, during which several witnesses observed an unusual “wiggle” in the rear of the airplane and heard a droning noise from the propeller with fluctuating pitch. The airplane then stalled and subsequently impacted a field in a level attitude. The witness reported that the pilot did not perform any unsafe flight maneuvers and both witness statements and recorded data indicated the engine was producing power throughout the flight. Postaccident examination of the engine revealed evidence of power at the time of impact and no indications of preimpact internal mechanical malfunctions. However, during recent maintenance the engine had been removed and reinstalled with improper washers. Although the engine remained within the cowling, it was partially separated from the engine mount. All four engine mount bolts and nuts were present and tight, but the required bushings and large-area washers on the engine side of the mount were missing. Both upper engine vibration isolator bolts lacked the required washers beneath the nuts, and the upper two engine mount bolt/nut assemblies appeared to have pulled through their respective rubber vibration isolators. The two lower engine mount bolts were severely bent and exhibited thin, non-aircraft-grade washers with hex-shaped extrusion marks indicative of the nuts bearing against the washers under load. Two of the nonstandard washers were recovered within the engine cowling near the lower attachment points. This improper installation resulted in the partial separation of the engine which likely degraded the handling characteristics of the airplane; however, the investigation could not determine the degree of degradation. The airplane’s degraded controllability, combined with the pilot’s exceedance of the airplane’s critical angle of attack when maneuvering, resulted in an aerodynamic stall and loss of control at an altitude too low for recovery. Postmortem toxicological testing detected ethanol at 0.038 g/dL in the pilot’s blood and at 0.01 g/dL in his urine; ethanol was not detected in vitreous fluid. Based on the fact that ethanol was not detected in vitreous fluid, that ethanol was detected only at a very low level in urine, and that markers of likely postmortem microbial activity were detected in blood, it is likely that at least some of the detected ethanol was from postmortem sources and it is unlikely that ethanol effects contributed to the accident. Additionally, toxicology results indicated that the pilot had used the sedating antihistamine medication diphenhydramine andcould have been experiencing associated cognitive and psychomotor impairment at the time of the accident. However, due to diphenhydramine’s potential for postmortem redistribution, the investigation was not able to determine whether the pilot may have been impaired by diphenhydramine at the time of the accident.

The pilot owned the airplane and interviews with witnesses and friends of the pilot indicated that the accident flight was the first following replacement of the propeller governor with a new unit. Access for the governor replacement required removal of the rear-mounted pusher-configuration engine from its truss mount. According to one individual interviewed, the pilot had removed and replaced the engine. The individual, who was not a mechanic, said that he had assisted the pilot but that his involvement was limited. The airplane’s maintenance logbooks were not located. On September 29, 2023, about 1200 eastern daylight time, an experimental amateur-built Smith Cozy Mark IV, N95SF, was substantially damaged when it was involved in an accident near Cullman, Alabama. The airline-transport-rated pilot was fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to a friend of the pilot, who also witnessed the accident, he had spoken with the pilot earlier on the day of the accident. The pilot told him that he had recently replaced the airplane’s propeller governor and planned to fly over to the witness’s field. The witness stated that the pilot occasionally did a flyby to “say hello” and did not perform any unsafe maneuvers during these visits. The witness said that, while he was working outside, he heard the airplane approaching and observed it arriving from the east. He and other witnesses observed that the airplane turned north, then south, and conducted a low pass. The pilot waved from the cockpit before initiating a climbing left turn. During the airplane’s turn, the witnesses observed an unusual “wiggle” in the rear of the airplane and heard a droning noise from the propeller with fluctuating pitch. The airplane then appeared to stall, and it subsequently impacted a field in a level attitude. The Cullman County, Alabama, Medical Examiner’s Office performed an autopsy on the pilot. The cause of death was determined to be blunt force trauma. Toxicological testing was performed by the FAA Forensic Sciences Laboratory. Postmortem toxicological testing by the FAA Forensic Sciences Laboratory detected ethanol at 0.038 g/dL in blood and at 0.01 g/dL in urine; ethanol was not detected in vitreous fluid. N-butanol and n-propanol were detected in blood and were not detected in urine or vitreous fluid. Diphenhydramine was detected at 197 ng/mL in blood and at 3592 ng/mL in urine. Glucose was measured at 680 mg/dL in urine and at 14 mg/dL in vitreous fluid. The airplane was equipped with an EDM-900 engine monitoring system. The EDM-900 engine monitor data included exhaust gas temperatures, cylinder head temperatures, oil temperature, oil pressure, fuel flow, and engine rpm. The data indicated that the engine was producing power throughout the accident flight and that recorded parameters were consistent with expected operating ranges. The final seconds of data showed a rapid decrease in rpmand fuel flow, consistent with a sudden loss of power associated with ground impact. The airplane impacted terrain in a flat attitude in a field. Several propeller strikes were observed along the wreckage path. The wooden MT three-blade propeller remained attached to the hub, and all three blades were splintered. The fuselage was fractured, and both wing assemblies were displaced aft at the inboard fuel tanks. Inside the cockpit, the throttle, mixture, and propeller controls were intact, but their ends were bent. The associated control cables remained attached and, when manipulated, their respective engine controls moved through full travel. The fuel selector was found positioned to the right fuel tank, which contained more than 5 gallons of fuel. A fuel sample from the tank was blue in color and free of debris. Fuel obtained from the source where the airplane was last refueled also tested satisfactory. No anomalies were noted with the fuel system. All flight control surfaces remained attached to the airframe, and control continuity was established from the cockpit to each surface. No anomalies were observed in the flight control system that would have precluded normal operation. The engine remained within the cowling but was partially separated from the engine mount. All four engine mount bolts and nuts were present and tight, but the required bushings and large-area washers on the engine side of the mount were missing. Both upper engine vibration isolator bolts (truss mount to engine case) lacked the required washers beneath the nuts. The upper two engine mount bolt/nut assemblies appeared to have pulled through their respective rubber vibration isolators. The two lower engine mount bolts were severely bent and exhibited thin, non-aircraft-grade washers with hex-shaped extrusion marks. These marks were consistent with the nuts bearing against the washers under load. Two of the nonstandard washers were recovered within the engine cowling near the lower attachment points.