CEN23FA204

An in-flight breakup due to structural overload of the airplane for undetermined reasons.

The pilot, who was the owner and builder of the experimental, amateur-built airplane, departed with a pilot-rated passenger on a 15 to 20-minute local flight. Witnesses reported that the airplane broke up in flight and descended to the ground. The debris path extended for about 1,435 ft, beginning with debris from the wings, consistent with failure related to the wing structure. Postaccident examination of the engine and propeller revealed no mechanical anomalies that would have precluded normal operation. No preimpact flight control deficiencies were found. There was no evidence of flutter. The wing separations were consistent with upward and aft bending and/or torsional loading based on deformation signatures of the wing attachment brackets, strut brackets, and front strut attachment fittings (outboard end). Fracture surfaces of the wing attachment brackets and front strut fittings were consistent with overstress separation. No flight track information was available for the accident flight. The pilot built the airplane based on dimensions from another airplane for which no plans had been produced. The accident airplane was issued a special airworthiness certificate about 21 years before the accident. At the time of the accident, the airplane had been modified from its original configuration with the installation of a heavier, higher-horsepower engine and the installation of a different propeller. Because no maintenance records were located for the airplane, there was no information available regarding this modification, the airplane’s operational time, or its inspection/maintenance history. The airplane’s design/build plans were not based upon a structural engineering analysis to determine a structural design envelope, structural loads, or structural performance. Accordingly, the basis for any design safety margins and limitations are unknown. There were no regulatory design requirements for the airplane due to its experimental classification. Metallurgical examination revealed no conclusive evidence of pre-existing or progressive damage signatures that would have initiated the accident, and fractured structural components were consistent with overstress separation. One small area of possible fatigue fracture was observed emanating from the weld face on the lower-forward left strut end fitting at the outboard end; however, based on the amount of deformation observed in this area, it was not a likely fracture initiation point. The pilot’s toxicological testing detected several volatile solvents; however, the volatile solvent levels measured in the pilot’s tissues cannot be used to reliably predict the route of his exposure or specific effects. Thus, whether the pilot had inhaled volatile solvents recreationally or was experiencing any impairing effects of volatile solvent exposure, could not be determined. Toxicological testing also detected ethanol in liver tissue; n-butanol (a potential indicator of postmortem microbial activity) was also detected in this specimen; however, it is likely that the detected ethanol was from sources other than alcohol consumption and did not likely contribute to the accident. The pilot’s toxicology results also demonstrated the presence of central nervous system depressant medications, including cyclobenzaprine and gabapentin. Cyclobenzaprine use may be associated with significant performance impairment. Use of gabapentin can also increase the user’s somnolence, dizziness and fatigue, potentially impairing pilot performance. Both cyclobenzaprine and gabapentin have potential postmortem redistribution; therefore, reliably associating levels with impairing effects is not possible. Overall, whether the pilot’s use of cyclobenzaprine and gabapentin contributed to the accident cannot be determined. The pilot-rated passenger’s mild-to-moderate coronary artery disease conveyed some increased risk of a sudden impairing or incapacitating cardiac event, including angina, arrhythmia, or heart attack. There is no autopsy evidence that such an event occurred. However, such an event does not leave reliable autopsy evidence if it occurs immediately before death. The aircraft was configured such that it could be controlled from either the left or right front seat. Thus, it is unlikely that the pilot-rated passenger’s coronary artery disease contributed to the accident. In addition, the pilot-rated passenger’s toxicological testing indicated use of citalopram and diazepam. Citalopram and diazepam, and conditions that may be treated with these medications, can adversely affect pilot performance and judgment. However, it is unclear if the pilot-rated passenger’s performance or judgment were a factor in the outcome; whether effects of the pilot-rated passenger’s use of citalopram and diazepam or of any associated underlying conditions contributed to the accident cannot be determined. Although the available information is consistent with an in-flight failure of the wing structure due to overload, given the lack of flight track information or recorded data from onboard the airplane, the circumstances of the in-flight breakup could not be determined.

The accident airplane, a Luce Buttercup, was built by the accident pilot based on dimensions from the original Wittman Buttercup, for which there were no plans produced. The accident pilot produced and sold his own plans for the Luce Buttercup based on the original Wittman design. The Luce Buttercup plans were not based upon a structural engineering analysis to determine a structural design envelope, structural loads, or structural performance. Accordingly, the basis for any design safety margins and limitations are unknown. There were no regulatory design requirements for the Luce Buttercup due to its experimental classification. The plans stated: WARNING: These drawings are that of Steve Wittman’s design. I am not an engineer just a hobbyist. I have reproduced this plane from dimensions taken from the original Buttercup. Any changes that have been made incorporated items from Wittman’s later aircraft; i.e. Tailwind. You as a builder are solely responsible for the craftmanship and the outcome of your project… During an initial application for a special airworthiness certificate as an experimental amateur-built aircraft, the Federal Aviation Administration (FAA) inspector from the Rochester Flight Standards District Office found 20 discrepancies during the airplane’s initial certification inspection. A special airworthiness certificate was issued in December 2001 after the discrepancies were resolved. The airplane’s special airworthiness certificate application records in 2001 showed the airplane was equipped with a Continental O-200-A engine, with a maximum continuous horsepower rating of 100 and a dry weight of 190 lbs, and an Aymar-DeMuth propeller. The application listed the airplane’s maximum gross weight as 1,350 lbs. Payload was 531 lbs, and fuel capacity was 20 gallons. The empty weight was 819 lbs. The cruise speed was 135 mph, and its top speed was 155 mph. The never-exceed speed listed was 170 mph. At the time of the accident, the airplane was modified from its original configuration with the installation of a Lycoming O-290-D2, which produced 135 horsepower and weighed 233 lbs, and a Prince Aircraft Company propeller. The airframe, engine, and propeller logbooks for the accident airplane were not located; its operational flight times and inspection history could not be determined. Airman medical records showed the weight of the pilot as 212 lbs and the weight of the pilot-rated passenger as 170 lbs. The fuel quantity at the time of the accident and the airplane’s gross weight could not be determined. According to the FAA medical case review, the 69-year-old pilot’s last aviation medical examination was May 2, 2016. At that time, he reported high blood pressure and seasonal allergies. He reported taking the medications lisinopril/hydrochlorothiazide, amlodipine, omeprazole, and loratadine. The aviation medical examiner (AME) noted that the pilot’s high blood pressure was qualified under Conditions AMEs Can Issue (CACI) criteria. The pilot was issued a third-class medical certificate with the limitation that he must wear corrective lenses. The medical certificate expired in 2018. The pilot completed the requirements for operation under BasicMed in July 2022. The Office of the Medical Examiner of Monroe County, Rochester, New York, performed the pilot’s autopsy. According to the pilot’s autopsy report, his cause of death was diffuse blunt force trauma, and his manner of death was accident. Examination of his heart identified mild coronary artery disease. The remainder of the autopsy, including visual examination of the heart, did not identify other significant natural disease. NMS Labs performed postmortem toxicological testing of the pilot’s liver tissue. Cyclobenzaprine was detected at 320 ng/g. Ethanol was detected at 0.4 g/hg. Toluene was detected at 3 ng/g. O-xylene was detected at 2 mcg/g, m-xylene was detected at 3 mcg/g, and p-xylene was detected at 1.1 mcg/g (total o-, m-, and p-xylenes 6.1 mcg/g). Methyl ethyl ketone (MEK) was detected at 21 mcg/g. Chloroethane was detected at 11 mcg/g. N-butanol was detected at 10 mcg/g. Norcyclobenzaprine, acetaminophen, and caffeine were presumptively positive. The FAA Forensic Sciences Laboratory performed toxicology testing of postmortem specimens from the pilot. Cyclobenzaprine was detected in liver tissue at 195 ng/g and in muscle tissue at 13 ng/g. Norcyclobenzaprine was detected in liver tissue at 1,856 ng/g and in muscle tissue at 117 ng/g. Gabapentin was detected in liver tissue at 915 ng/g and in muscle tissue at 769 ng/g. Chlorothiazide was detected in liver tissue and not detected in muscle tissue. Hydrochlorothiazide, meloxicam, and acetaminophen were detected in liver and muscle tissue. Ethanol was not detected in brain or liver tissue. According to the FAA medical case review, the 72-year-old pilot-rated passenger’s last aviation medical examination was March 13, 2023. At that time, he reported high blood pressure, high cholesterol, and prediabetes. He reported taking the medications metformin, lisinopril, diltiazem, and atorvastatin. The AME noted that the passenger’s high blood pressure was qualified under CACI criteria. The AME issued the passenger a third-class medical certificate with the limitation that he must wear corrective lenses for near and distant vision. The passenger had a Statement of Demonstrated Ability (SODA) for defective color vision. The Office of the Medical Examiner of Monroe County, Rochester, New York, performed the pilot-rated passenger’s autopsy. According to the pilot-rated passenger’s autopsy report, his cause of death was diffuse blunt force trauma, and his manner of death was accident. Due to the extent of injuries, the brain was absent. Examination of the heart revealed coronary artery disease with up to 50% narrowing of the coronary arteries. The remainder of the autopsy examination, including visual examination of the heart, did not identify other significant natural disease. NMS Labs performed toxicological testing of liver tissue of the pilot-rated passenger. Citalopram (including escitalopram) was detected at 3600 ng/g. Diltiazem was detected at 3900 ng/g. Desmethylcitalopram/desmethylescitalopram (undifferentiated) and caffeine were presumptively positive. The FAA Forensic Sciences Laboratory performed toxicology testing of postmortem tissue specimens from the pilot-rated passenger. Citalopram was detected in liver tissue. Citalopram was also detected in muscle tissue at 257 ng/g. N-desmethylcitalopram was detected in liver and muscle tissue. Diazepam was detected in liver tissue at 72 ng/g and muscle tissue at 19 ng/g. Nordiazepam was detected in liver tissue at 284 ng/g and in muscle tissue at 73 ng/g. Oxazepam was detected in liver tissue at 16 ng/g and detected in muscle tissue at 4 ng/g. Temazepam was detected in liver tissue at 7 ng/g and was not detected in muscle tissue. Atorvastatin, meloxicam, and tadalafil were detected in liver and muscle tissue. Testing for diltiazem was inconclusive in liver tissue; diltiazem was detected in muscle tissue. Pramoxine was detected in liver tissue and was not detected in muscle tissue. The main wreckage of the airplane was located in a field and oriented on a magnetic heading of 150°. The engine and propeller were about 15 ft from the main wreckage and were embedded in the ground. The left and right wings came to rest about 1,285 ft east of the main wreckage. Internal wood wing pieces were located about 150 ft east/southeast of the wings. Examination of the engine and propeller revealed no mechanical anomalies that would have precluded normal operation. Flight control continuity from the control surfaces to their respective cockpit controls was confirmed. There was no evidence of flutter. The wing, wing struts, horizontal stabilizer with elevator, and propeller were sent to the NTSB Materials Laboratory for examination. The wing separations w