ERA24FA310

A sudden propeller overspeed and subsequent separation of the propeller blades and hub, while maneuvering at high speed and at low altitude, which resulted in a collision with a tree during the subsequent forced landing attempt.

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.

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. 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 widely marketed 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. 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 engine cowling 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