HENSLER HOWARD CASSUTT

Full Narrative

HISTORY OF FLIGHTOn August 23, 2023, about 1200 mountain daylight time, an experimental, amateur-built Cassutt airplane, N6291N, was substantially damaged when it was involved in an accident near West Jordan, Utah. The pilot was fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 test flight.
According to a witness, who was a pilot scheduled to race the accident airplane in an upcoming air race event, he did not know that the accident pilot was going to fly on the day of the accident. He reported that, until the day before the accident, the accident pilot had not flown the accident airplane in about 2 years and had been testing it in advance of an upcoming air race. After the flight the day before the accident, the accident pilot informed the witness that he observed the oil temperature was “pegged” at 280°F. On the day of the accident, the witness arrived at the airport when the accident pilot was getting ready to fly. While the engine was idling he noticed that the engine oil pressure was about 10 psi. He also learned that the pilot had changed the oil that day after he discovered some flakes in the oil screen. The witness noticed that the pilot seemed rushed on the day of the accident.
The witness stated that he was standing near the approach end of runway 16 at South Valley Regional Airport (U42), West Jordan, Utah, when he observed the accident pilot take off. He watched the airplane’s tail rise when the airplane was about 1,000 ft into its ground run, and the airplane lifted off the runway about 1,750 ft from the approach end of the runway. The airplane entered a climb and then started a right turn toward the crosswind leg of the airport traffic pattern. The right wing then rapidly dropped about 45° and the airplane entered a nose-down attitude. The airplane rolled wings level as it maintained a nose-down attitude, then it disappeared from the witness’ view.
Another witness observed the airplane take off and make an abrupt right turn before it “fell out of the sky” from about 150 ft above ground level.
Surveillance video from a nearby commercial building showed the airplane during its descent and final moments. The airplane appeared on a northwest heading as it rapidly descended from about 80 ft above ground level. The airplane maintained a slight left-wing- and nose-low attitude until it impacted a chain link fence and the ground.
No devices that retained data were recovered from the airplane and there was no ADS-B data for the accident flight. AIRCRAFT INFORMATIONAccording to the pilot’s wife, the pilot purchased the airplane around 2009 for the Reno Air Races, then sold it shortly thereafter. He re-acquired the airplane in 2013. The pilot would fly the airplane locally infrequently, as he flew his other two airplanes more often. She added that he had not flown the accident airplane for about four months before the accident.
The airplane was equipped with an experimental, air-cooled, horizontally opposed, 100-hp reciprocating engine. An invoice from Polymer Dynamics, Inc., dated June 30, 2023, indicated that the company coated multiple components from the accident engine with their proprietary coating. The coating manufacturer reported that their coatings are used for various purposes such as lubrication, heat control, oil retention, reduction in parasitic drag, heat transfer, and temperature control. The pilot’s social media web page contained a photographic chronology of coated engine components that started on May 27, 2023 and ended on August 11, 2023 with a photograph of the accident airplane with the engine installed. Certain components such as the crankshaft and pistons were shown with coatings on the pilot’s social media page; however, the coating manufacturer had no record of coating these parts under the pilot’s name. The pilot’s wife reported that he assembled the engine himself with occasional assistance.
According to the racer, the accident pilot had asked another mechanic to rebuild the engine for him; however, the mechanic declined due to other work, so the pilot performed the assembly and installation himself. The pilot had told his wife that if he “messed the engine up,” it should kill him instead of the racer.
According to the engine manufacturer, the oil pressure at idle is 10 psi and in flight is 30-60 psi.
Maintenance records and performance information for the airplane and engine were not available.
A friend of the pilot’s who helped him with an engine assembly (before the most recent overhaul) on the accident airplane noted that the pilot preferred tight clearances and even discovered scuffing on a piston skirt on one occasion. He also helped the accident pilot reconfigure the airplane’s tail from a conventional tail to a T-tail, which the pilot had designed and built. During flight testing following the reconfiguration, they discovered that, while in a turn, the pilot could completely lose elevator effectiveness until they accelerated. Further testing showed that the airplane would enter what the friend referred to as a “deadband” that could only be overcome by accelerating.
According to the Federal Aviation Administration Pilot’s Handbook of Aeronautical Knowledge (FAA-H-8083-25C),
When flying at a very high AOA [angle of attack] with a loss airspeed and an aft CG, the T-tail aircraft may be more susceptible to a deep stall. In this condition, the wake of the wing impinges on the tail surface and renders it almost ineffective. The wing, if fully stalled, allows its airflow to separate right after the leading edge. The wide wake of decelerated, turbulent air blankets the horizontal tail and hence its effectiveness diminished significantly. In these circumstances, elevator or stabilator control is reduced (or perhaps, eliminated) making it difficult to recovery from the stall. It should be noted that an aft CG is often a contributing factor in these incidents, since similar recovery problems are also found with conventional tail aircraft with an aft CG. AIRPORT INFORMATIONAccording to the pilot’s wife, the pilot purchased the airplane around 2009 for the Reno Air Races, then sold it shortly thereafter. He re-acquired the airplane in 2013. The pilot would fly the airplane locally infrequently, as he flew his other two airplanes more often. She added that he had not flown the accident airplane for about four months before the accident.
The airplane was equipped with an experimental, air-cooled, horizontally opposed, 100-hp reciprocating engine. An invoice from Polymer Dynamics, Inc., dated June 30, 2023, indicated that the company coated multiple components from the accident engine with their proprietary coating. The coating manufacturer reported that their coatings are used for various purposes such as lubrication, heat control, oil retention, reduction in parasitic drag, heat transfer, and temperature control. The pilot’s social media web page contained a photographic chronology of coated engine components that started on May 27, 2023 and ended on August 11, 2023 with a photograph of the accident airplane with the engine installed. Certain components such as the crankshaft and pistons were shown with coatings on the pilot’s social media page; however, the coating manufacturer had no record of coating these parts under the pilot’s name. The pilot’s wife reported that he assembled the engine himself with occasional assistance.
According to the racer, the accident pilot had asked another mechanic to rebuild the engine for him; however, the mechanic declined due to other work, so the pilot performed the assembly and installation himself. The pilot had told his wife that if he “messed the engine up,” it should kill him instead of the racer.
According to the engine manufacturer, the oil pressure at idle is 10 psi and in flight is 30-60 psi.
Maintenance records and performance information for the airplane and engine were not available.
A friend of the pilot’s who helped him with an engine assembly (before the most recent overhaul) on the accident airplane noted that the pilot preferred tight clearances and even discovered scuffing on a piston skirt on one occasion. He also helped the accident pilot reconfigure the airplane’s tail from a conventional tail to a T-tail, which the pilot had designed and built. During flight testing following the reconfiguration, they discovered that, while in a turn, the pilot could completely lose elevator effectiveness until they accelerated. Further testing showed that the airplane would enter what the friend referred to as a “deadband” that could only be overcome by accelerating.
According to the Federal Aviation Administration Pilot’s Handbook of Aeronautical Knowledge (FAA-H-8083-25C),
When flying at a very high AOA [angle of attack] with a loss airspeed and an aft CG, the T-tail aircraft may be more susceptible to a deep stall. In this condition, the wake of the wing impinges on the tail surface and renders it almost ineffective. The wing, if fully stalled, allows its airflow to separate right after the leading edge. The wide wake of decelerated, turbulent air blankets the horizontal tail and hence its effectiveness diminished significantly. In these circumstances, elevator or stabilator control is reduced (or perhaps, eliminated) making it difficult to recovery from the stall. It should be noted that an aft CG is often a contributing factor in these incidents, since similar recovery problems are also found with conventional tail aircraft with an aft CG. WRECKAGE AND IMPACT INFORMATIONThe airplane came to rest on a curb about 0.3 nautical miles southwest of the departure end of runway 16. All of the airplane’s major structures were accounted for at the accident site. An initial impact point was marked by a broken fence about 100 ft southeast of the main wreckage and airplane fragments were distributed along the wreckage path to the main wreckage. The fuselage structure comprised welded tube metal, which had fractured and partially separated from the engine firewall. The cabin area was breached, and the fuselage aft of the cabin area was partially separated. Both wings were separated from the fuselage and had come to rest on top of the fuselage. The T-tail empennage was partially detached from the fuselage. The elevators remained attached to the horizontal stabilizers and the rudder was attached to the vertical stabilizer. 
Postaccident examination of the engine revealed some metallic fragments in the oil screen. There was also pitting and corrosion on the walls of the Nos. 1, 2, and 4 cylinders, deterioration of the thermal coating at some of the valve faces, circumferential scoring at the connecting rod bearings and journals, and dark coloration and longitudinal scoring at each piston skirt. ADDITIONAL INFORMATIONAccelerated Stalls
The FAA describes an accelerated stall in the Airplane Flying Handbook (FAA-H-8083-3C):
The pilot rolls the airplane into a coordinated, level-flight 45° turn and then smoothly, firmly, and progressively increase the AOA [angle of attack] through back elevator pressure until a stall occurs. Alternatively, the pilot rolls the airplane into a coordinated, level-flight 45° turn at an airspeed above VA or VO. After the airspeed slows to VA or VO, and at an airspeed 5 to 10 percent faster than the unaccelerated stall speed, the pilot progressively increases the AOA through back elevator pressure until a stall occurs. The increased back elevator pressure increases lift and the G load. The G load pushes the pilot’s body down in the seat. The increased lift also increases drag, which may cause the airspeed to decrease. The pilot should know the published stall speed for 45° of bank, flaps up, before performing the maneuver. This speed is typically published in the AFM. MEDICAL AND PATHOLOGICAL INFORMATIONThe Office of the Medical Examiner, Utah Department of Health and Human Services, performed the autopsy of the pilot. According to the autopsy report, the pilot’s cause of death was blunt force injuries, and the manner of death was accident. Coronary artery disease was identified, including 75% narrowing of the left anterior descending coronary artery by plaque. The remainder of the exam, including visual examination of the heart, did not identify other significant natural disease.
The Office of the Medical Examiner, Utah Public Health Laboratories, Forensic Toxicology Laboratory performed toxicological testing of postmortem femoral blood of the pilot. No tested-for substances were detected. TESTS AND RESEARCHOil Testing
Two oil samples were sent to an independent, third-party laboratory for analysis to determine the oil type and weight and if there were any metal/contaminants present. One sample was from oil wash drained by the pilot from the accident airplane and the other sample was from a jug presumed to be oil that the pilot used; these were labeled “Sample 1 (pilot oil)” and “Sample 2 (oil wash drained).”
The test results indicated that both samples were similar oils, but not the same. Sample 2 showed a high degree of wear/age and significant particulate contamination, while sample 1 showed some wear and aging, but was still within specification.
The crankshaft, connecting rods, bearing shells, camshaft, cylinders, pistons, and wrist pins were analyzed by the NTSB materials laboratory.
The outer edge of the propeller flange on the crankshaft was marked “M010M/020P,” indicating that the main journals were ground 0.01 inches undersize and the rod journals were ground 0.02 undersize. Identification marks found on the propeller flange pointed to a work order from Aircraft Specialty Services, which showed that the crankshaft was overhauled in 1976, at which time the main and rod journals were ground.
The crankshaft was intact and did not exhibit any evidence of a fracture; however, the surface of the main and connecting rod journals contained evidence of a circumferential wear pattern that corresponded with the contact areas of the bearing shells. There was no evidence of scoring or fractures at any of the journals and the oil passages were free of obstructions.
The steel backing layer for four of the connecting rod bearing shells were 0.020 inches below standard size and the steel backing layer for one of the main bearing shells was 0.010 inches below standard size. The inner surface of the bearing shells for the cylinder Nos. 1 and 2 main journals displayed a circumferential recessed groove at the center and the cylinder No. 3 main journal exhibited 5 recessed grooves. Several of the bearing shell inner surfaces contained severe wear damage that exposed the copper layer.
Scoring marks were observed throughout the combustion chambers of cylinder Nos. 1 through 4. Each of the scoring marks were parallel to the length of the chambers. The coating was peeling from the combustion face of most of the exhaust valves with exception of the cylinder No. 4 valve.
Longitudinal scoring marks were observed along the sidewalls of each piston, the outer walls of the piston rings, and the piston skirts below the rings all exhibited scoring marks parallel to the longitudinal axis of the cylinder.