ERA24FA310

The pilot, who was the builder of the experimental amateur-built airplane, was conducting a post-maintenance test flight. After performing several aerobatic maneuvers near the airport, the pilot began a high-speed low pass over the runway. Upon passing most of the runway, the airplane began a climb. A witness heard the engine go to a high rpm and then saw the entire propeller hub break apart. After the propeller hub fractured and separated, the airplane began a left turn toward a road. While maneuvering toward the road, the airplane’s left wing impacted a tree and the airplane subsequently rolled over and impacted terrain. Onboard recorded data revealed that, at the time the propeller separated, the engine was operating at 6,813 rpm, which equated to a propeller speed of 3,585 rpm. This speed was considerably in excess of the propeller blade blank manufacturer’s limit of 2,100 rpm. This speed would have produced a centrifugal force that was more than 3 times the design limit of the propeller blade blanks. Further examination of the onboard data revealed that, around the time of the propeller overspeed, the airplane was traveling at an airspeed about 223 miles per hour (mph); the published never-exceed speed (Vne) for the airplane was 215 mph. The data also revealed a sudden decrease in the longitudinal load factor, consistent with a sudden deceleration of the airplane, followed shortly thereafter by the longitudinal load factor returning to normal. A possible reason for the deceleration was a sudden increase in drag from the propeller blades moving to low pitch. This was followed by a reduction in drag on the airplane, which was likely due to the propeller separating from the airplane. Postaccident examination of the propeller governor, governor adapter, and the propeller gearbox revealed no evidence of any preacident mechanical failures or malfunctions that would have precluded normal operation. Ultimately, the reason for the propeller overspeed could not be determined based on available information.

On July 21, 2024, at 1754 eastern daylight time, an experimental amateur-built Titan T-51 Mustang airplane, N751TX, was substantially damaged when it was involved in an accident near Geneva, Ohio. The commercial pilot was fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. A witness to the accident, who also held a private pilot certificate, reported that the accident pilot performed maintenance on the airplane before the accident flight, including work on the pitot-static system and a fuel filter replacement. The witness reported that the accident pilot completed a few engine run-up checks and ground taxi runs, which appeared normal. Following the engine run-ups, the pilot checked the engine oil, noticed it was low, and subsequently added oil. The accident pilot then departed for a brief flight to ensure that everything was functional. The witness observed the accident pilot perform several maneuvers over the airport, including aileron rolls. The witness then observed the airplane descend to approach runway 1 to conduct a low pass. He observed the airplane fly over the majority of runway 1, then engine power increased, and the airplane pitched up into a pull-up maneuver, starting the climb near where he was standing next to the runway. When the airplane pitched up, he heard the engine go to a “super high rpm” and then the “entire prop hub” shattered. He observed several pieces separate from the nose section of the airplane, and the engine noise subsequently went silent. The witness observed the airplane turn left and complete a 180° turn, descending toward a road that was about 1/4 mile west of the runway, eventually turning out of his view while flying southbound. He believed that the pilot was navigating toward the road to the west of the airport to complete an emergency landing. According to a witness who was driving his vehicle northbound on the road about 1/4 mile west of the airport, he heard the sound of an airplane engine that seemed to be “over spooling.” He continued his northbound drive and observed the accident airplane approaching the road directly toward him flying southbound. The driver pulled off the road to the west, and about the same time, he observed the airplane maneuver slightly to the east. Shortly thereafter, he observed the airplane’s left wing “clip” an elevated tree branch that was near the road. The airplane rolled over and impacted terrain inverted. The witness observed that the airplane’s right landing gear was down, the left landing gear appeared to be in transit and coming down, and airplane’s wings were wobbling up and down. The witness at the airport recorded a video of the pilot’s runway flyover. The video recorded the airplane approaching runway 1 a few hundred feet above ground level. The engine sound increased during the pull-up, the airplane entered a shallow left bank, and an explosion could be seen and heard originating from the forward enginecowling area. The figure (below) shows the video frame-by-frame during the parts separation; the red circles outline the four propellers separated from the propeller hub. Figure. Frame-by-frame view of the parts separation (the red circles outline the four propellers) Data retrieved from onboard avionics that contained nonvolatile memory revealed that, 22 seconds before the end of the recording, the engine speed increased to 6,813 rpm, which was calculated to be a propeller speed of 3,585 rpm. According to the manufacturer of the propeller blade blanks (the composite portion of the propeller blade excluding the metallic collar that would interface with the propeller hub), the centrifugal force of one blade at the design limit speed of 2,100 rpm was 10,500 lbs. At a speed of 3,585 rpm, the centrifugal force on the propeller was 30,600 lbs. Additional recorded data was consistent with the witness report that the pilot conducted several aerobatic maneuvers during the accident flight. Some of the maneuvers included negative load factors; however, during the last 1.5 minutes of flight, the load factor on the airplane remained positive. The data also revealed that, around the time of the propeller overspeed, the airplane was traveling at an airspeed of 223 miles per hour (mph). According to the manufacturer, the published Vne for the Titan T-51 was 215 mph. The recorded data also revealed a sudden decrease in the longitudinal load factor consistent with a sudden deceleration of the airplane, followed shortly thereafter by the longitudinal load factor returning to normal. An autopsy was performed on the pilot by the Cuyahoga County Medical Examiner’s Office. According to the report, the cause of death was blunt force injuries. The autopsy report identified coronary artery disease, with 70% narrowing of the left anterior descending coronary artery, 50% narrowing of the right coronary artery, and 30% narrowing of the left circumflex coronary artery by plaque. The left ventricle of the heart was described as thickened. Visual examination did not identify other significant natural disease of the heart muscle. The aortic valve was calcified. The aorta contained extensive erosive calcific plaques. The bilateral middle cerebral arteries of the brain contained nonocclusive plaques. The kidneys displayed some tissue changes of the type that may be seen with chronic high blood pressure. Postmortem toxicological testing detected cannabidiol (CBD) and 7-carboxy-CBD in cavity blood and urine. 7-hydroxy-CBD was detected in urine and was not detected in cavity blood. Losartan and hydrochlorothiazide were detected in cavity blood and urine. Chlorothiazide was detected in urine; chlorothiazide testing in cavity blood was inconclusive. Desmethylsildenafil was detected in urine and was not detected in cavity blood. Ibuprofen was detected in cavity blood and urine. CBD is a non-intoxicating biologically active chemical contained in the cannabis plant. CBD also is widelymarketed in a variety of products for a variety of claims. CBD in such products often is derived from cannabis, but CBD also may be chemically synthesized. The only CBD product approved by the US Food and Drug Administration is a prescription medication for the treatment of certain seizure disorders. The purity and safety of other CBD products is generally uncertain, and CBD products may contain contaminants (including delta-9-THC). The chemical CBD itself does not typically cause impairment on objective measures of performance. CBD use is not specifically disqualifying for pilot medical certification. However, the FAA's Guide for Aviation Medical Examiners notes that some conditions for which people use CBD products may be disqualifying, and instructs examiners to review a current detailed clinical progress note to verify any underlying condition. 7-hydroxy-CBD and 7-carboxy-CBD are metabolites of CBD. Losartan and hydrochlorothiazide are prescription medications commonly used to treat high blood pressure. Chlorothiazide may be present as an impurity in hydrochlorothiazide from the manufacturing process; chlorothiazide also is available as a prescription diuretic medication that can be used in the treatment of edema and high blood pressure. Losartan, hydrochlorothiazide, and chlorothiazide are not generally considered impairing. The pilot did not report high blood pressure or medication use at his last aviation medical examination. Desmethylsildenafil is a metabolite of sildenafil (which was not detected in this case). Sildenafil is a prescription medication commonly used to treat erectile dysfunction, as a sexual enhancement aid, or in the treatment of certain other conditions, including pulmonary hypertension. Sildenafil is not typically impairing, although the FAA states that pilots should wait 8 hours after using it before flying, to monitor for side effects. Ibuprofen is an anti-inflammatory medication that is available over the counter and is commonly used to treat pain and fever. Ibuprofen is not generally considered impairing. According to FAA airman records, the pilot held a commercial pilot certificate with ratings for airplane single-engine land and sea. He also held a flight instructor certificate as well as a repairman — experimental aircraft builder for the accident airplane. He reported 12,500 flight hours at the time of his most recent FAA medical examination in October 2023, and 100 hours logged within the six months before the examination. The main wreckage came to rest inverted in a wooded area about 30 ft east of a county road. The initial impact point coincided with elevated tree branches about 250 ft north of the main wreckage. The debris path was oriented on a 155° magnetic heading. All portions of the airframe were located in the debris path. The outboard portion of the left wing and aileron were co-located with the initial impact point. The outer portion of the right wing and right aileron were co-located with a secondtree impact closer to the main wreckage. The engine remained attached to the fuselage. There was no evidence of fire. Flight control continuity was confirmed from the flight controls to breaks consistent with impact-related forces for all control surfaces. The right landing gear was found extended and locked and the left landing gear was found partially extended. The throttle and propeller arms remained functional. The throttle lever was found pulled mostly aft toward the idle power position. The propeller control was found full forward. There were no anomalies observed with the airframe that would have precluded normal operation. The engine displayed impact damage signatures, with most of the damage observed to the forward portion of the engine, intake manifold, and rocker arm covers. The propeller reduction gearbox had fracture-separated from the engine and displayed impact damage signatures. A portion of the fractured propeller hub remained attached to the propeller driveshaft. Both valve keepers for the No. 1 exhaust valve were separated from the valve and spring assembly, and one of the valve keepers for the No. 3 intake valve had also separated. The keepers were found in the rocker box assembly and appeared to be undamaged. The No. 1 exhaust valve was seized in the valve guide. Upon further examination, the No. 1 exhaust valve was found to be bent, and the No. 1 piston displayed semicircular impressions consistent with multiple valve strikes with the No. 1 exhaust valve. The damage observed to the valve and piston was consistent with a floating valve, which can occur during an engine overspeed. The rest of the rocker arms, valves, and valve springs displayed normal operating and lubrication signatures. The pistons and cylinders displayed varying amounts of corrosion and contamination consistent with postaccident water intake. The crankshaft remained intact and, after removing the cylinder heads, rotated without signs of binding. The connecting rods remained attached to their journals and displayed normal operating and lubrication signatures. The camshaft and lifters were removed and the components displayed normal operating and lubrication signatures. The oil sump remained intact and appeared to be undamaged. The sump was removed, and contained an unquantified amount of fluid consistent with engine oil. The oil pickup tube remained attached to the oil pump, and there were no obstructions observed. The oil pump was removed; the pump drive gear rotated without any binding and the pump was capable of pumping residual oil. The throttle body remained attached to the induction manifold and displayed minor impact damage. The throttle control arm was capable of normal movement and the throttle valve actuated normally. The propeller gearbox had separated from the rest of the engine and displayed impact damage. A small amount of residual gearbox oil was within the gearbox housing. Continuity was established within the gearbox by rotating thedriveshaft and observing propeller shaft movement. The reduction gearbox was disassembled and the internal components displayed normal operating and lubrication signatures. The propeller governor drive adapter had separated from the reduction gearbox and displayed impact damage. The adapter drive gear to governor drive gear continuity was established by rotating the adapter drive gear. The propeller governor adapter oil galleys were clear of obstructions. The propeller governor had minor impact damage. The propeller governor drive was rotated manually. There were no signs of binding during rotation, and the pump could be heard pumping residual oil. The propeller governor was placed on a test bench, and the governor operated normally. The propeller hub was fractured into multiple pieces; a portion of the hub remained attached to the reduction gearbox. The other portions of the hub were located on the ground around the airplane’s flight path. The propeller blades were marked with “A”, “B”, “C”, and “D” for identification purposes. The propeller blade marked “A” remained intact and had separated from the propeller hub. There was a portion of impact damage about 3/4 of the propeller’s length. The propeller blade marked “B” remained attached to a portion of the separated propeller hub and had impact damage to the propeller blade. Both propeller blades marked “C” and “D” had separated at the propeller shank and displayed impact damage at the leading edge of the propeller blades. The damage to propeller blades “C” and “D” was consistent with an overspeed event.