N18263

HISTORY OF FLIGHTOn May 28, 2023, at 1815 eastern daylight time, an experimental, amateur-built Luce Buttercup, N18263, was destroyed when it was involved in an accident near Lyndonville, New York. The pilot and pilot-rated passenger sustained fatal injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

On the day of the accident, the pilot provided airplane rides during a picnic using another airplane. The pilot-rated passenger told the pilot that he wanted to go flying, so the pilot conducted a preflight inspection of the accident airplane, and they departed on the accident flight, which was to be about 15 to 20 minutes in duration. The pilot was seated in the left seat and the pilot-rated passenger was seated in the right seat.

A witness stated that he heard a low-flying airplane flying toward the southwest and then saw some pieces of the airplane falling into an orchard just south of his home; he then lost sight of the airplane. A second witness saw the airplane flying southeast and banking right. The second witness stated that when the airplane leveled off, the left wing came off the airplane, followed by the right wing. The airplane then spun into a field.

There was no flight tracking data associated with the airplane. AIRCRAFT INFORMATIONThe 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. AIRPORT INFORMATIONThe 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. WRECKAGE AND IMPACT INFORMATIONThe 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 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. The thickness of the rear spars was consistent with dimensions specified on the Luce Buttercup drawings.

The outboard end of the fractured left front strut bracketed area is shown in Figure 1. A relatively flat crack was observed extending through the weld from the weld face. Above this region, dimpled fracture features were observed, consistent with overstress separation. Faint fracture features in a small area, which resembled fatigue striations, were observed at higher magnification as shown in Figure 2.

Figure 1. Digital microscope images of the left front strut fracture location near the strut bracket connection. A closer view of the bracketed region is shown on the right. A relatively flat crack was observed extending through the weld from the weld face in the area indicated by the yellow dashed line.

Figure 2. Scanning electron microscope images of the relatively flat fracture region identified in the previous figure. Faint horizontal features resembling fatigue striations are indicated by yellow arrows with the crack growth direction from bottom to top in this image. ADDITIONAL INFORMATIONAn original Wittman Buttercup located in an Experimental Aircraft Association Museum was inspected by the NTSB IIC. There were no plans/design drawings by Steve Wittman for the Wittman Buttercup. The Wittman Buttercup did not have inspection ports that could be used to gain access into the aircraft’s internal structure, which limited the non-destructive documentation of design details of the structure. The aircraft made use of a structural compression rib at its sixth rib. The wingtip of the aircraft was shaken by hand to visually compare its response to that of a Luce Buttercup that was in the area. The Luce Buttercup wingtip was shaken by hand and a qualitative response difference to that of the museum Wittman Buttercup was difficult to make. The workmanship, build methods, materials used, and design variations of the comparative Luce Buttercup are unknown. MEDICAL AND PATHOLOGICAL INFORMATIONAccording 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 Con...