Accident Sequence
On February 3, 2008, at about 1617 eastern standard time, an experimental amateur-built RV-4, N580RG, crashed while maneuvering at Elkin Municipal Airport (ZEF), Elkin, North Carolina. The flight was operated as a personal flight under 14 CFR Part 91. Visual meteorological conditions prevailed, and no flight plan was filed. The airplane was substantially damaged by impact and a postcrash fire, and the commercial pilot, the sole occupant, was killed. The flight originated about 1612 from Elkin Municipal Airport.
The accident pilot and the pilots of two other airplanes departed from runway 07. After takeoff, the accident pilot turned downwind, base, and final for runway 07 and performed a low pass flying over the runway at an estimated altitude of 8 feet above ground level. Witnesses reported that when the flight was near the departure end of runway 07, the airplane pitched up and rolled left while continuing to climb. One pilot-rated witness reported that at the top of the climb at about 250 to 300 feet agl, the airplane appeared to perform a "split s" type maneuver, and the pilot appeared to have dished out of the roll. The airplane began descending in a nose-low attitude. Before losing sight of the airplane due to obstructions, it was flying nearly perpendicular to the runway and began a rapid nose-up pitch change. The witness then observed a fireball.
Pilot Information
The pilot, age 64, held a commercial pilot certificate with an airplane single engine land rating issued September 12, 1969, and held a third-class medical certificate issued March 1, 2006, with a limitation to have available glasses for near vision. The pilot's logbook was not located; he listed 2,050 hours total time on his last medical certificate application.
Aircraft Information
The amateur-built airplane was manufactured in October 1993 as model RV-4, serial number 2148. It was powered by a Lycoming O-320-B3B 160-horsepower engine and equipped with an Edward Sterba 68-70 wood fixed-pitch propeller. The pilot purchased the airplane on September 20, 2005. Maintenance records were not located; no determination could be made as to when the last condition inspection occurred.
Meteorological Information
A surface observation weather report taken at Wilkes County Airport (UKF), North Wilkesboro, North Carolina, at 1621, about 4 minutes after the accident, indicated wind from 070 degrees at 3 knots, visibility 10 statute miles, clear skies, temperature and dew point 15 and minus 2 degrees Celsius, altimeter 30.17 inches of mercury. The accident airport was located 084 degrees and 15.5 nautical miles from UKF.
Communications
ZEF airport is equipped with a common traffic advisory frequency (CTAF) of 123.05 MHz, which is not recorded. There is no information that the pilot announced on the CTAF his intention of performing low-level aerobatics.
Airport Information
ZEF airport has one runway designated 07/25.
Wreckage and Impact Information
Examination of the departure end of runway 07 revealed ground scars on grass south of the south edge of runway 07/25. The ground scars were oriented on a magnetic heading of 164 degrees. The first ground scar was located about 16 feet south of the south edge of the runway. Several marks on the grass continued to a berm located about 47 feet from the south edge of the runway. Pieces of wooden propeller blade were located at the berm. Gray-colored paint was noted at the ground scars. The airplane came to rest inverted in an area of lower elevation south of the runway. Fire damage to the ground was noted between the berm and the final resting point.
Examination of the airplane revealed the cockpit, fuselage, and inboard portion of both wings were consumed in the postcrash fire. All components necessary to sustain flight remained attached. Examination of the rudder and elevator flight control system revealed no evidence of preimpact failure or malfunction. Examination of the aileron flight control system revealed the left and right aluminum pushrod assemblies (Control Stick to Bellcrank, P/N W-416) were consumed by fire in each wing root area; however, each respective rod end that connects to the rear control stick remained connected at the stick. The remaining sections of the left and right pushrod assemblies were connected at each aileron bellcrank. Further examination revealed the right pushrod assembly (P/N W-418) was connected at the bellcrank and at the control surface. The left pushrod assembly (P/N W-418) was connected at the bellcrank but was separated from the rod end that remained connected to the control surface. Comparison of the left and right pushrod assemblies (P/N W-418) revealed the threaded rod ends at each end of the right tube were secured by two rivets 90 degrees apart, while only the threaded rod end at the left bellcrank was secured by rivets. The threaded rod end for the left pushrod assembly near the control surface was not secured by rivets. The left pushrod assembly and rod end were retained for further examination.
Examination of the engine with FAA oversight revealed crankshaft, camshaft, and valve train continuity during hand rotation. Fire damage precluded an engine run. Magnetos and carburetor were heat damaged, precluding bench testing. Spark plug electrodes were light gray, consistent with normal fuel/air metering. No evidence of preimpact failure or malfunction of the engine or engine accessories was noted.
Examination of the two-bladed wood propeller attached to the engine revealed both blades were shattered and heat damaged to the root ends. Sections of propeller blade were noted at the initial ground impact location.
Medical and Pathological Information
A postmortem examination of the pilot was performed by Wake Forest University School of Medicine Department of Pathology. The cause of death was "blunt force injuries to head and torso." The autopsy report did not indicate the pilot was wearing a parachute. Forensic toxicology was negative for carbon monoxide, cyanide, volatiles, and tested drugs.
Additional Information
The pilot landed at ZEF approximately 1.5 hours earlier, and prior to landing, the accident pilot performed a low pass over runway 25. When past the departure end of runway 25, the accident pilot performed a "poorly executed aileron roll." After completing the roll, the accident pilot landed uneventfully on runway 25 and secured the airplane. There was no evidence the pilot reported on the CTAF an intention to perform low-level aerobatics. The airport manager, also a pilot, was at the airport but did not discuss the low-level aerobatics with the accident pilot.
Examination of the left pushrod assembly (P/N W-418) by the NTSB Materials Laboratory revealed the rod end and threaded rod end assembly exhibited a bend of about 3 degrees centered where the thread portion joined the plain diameter portion. There were no holes in the tube or evidence of welding securing the threaded rod end to the steel tube. No marks on the plain diameter portion indicated extraction had occurred at intervals during operation prior to impact.
Safety Board review of the engineering drawing for the pushrod assembly (P/N W-418) bellcrank to aileron revealed that two AN470AD4-12 rivets are required to secure each threaded rod end to each end of the steel tube, though the drawing only depicts rivets at the end closest to the aileron. The opposite end depicts an option to weld instead of rivets.
Review of 14 CFR Part 91.303 indicates no person may operate an aircraft in aerobatic flight below 1,500 feet above the surface. Aerobatic flight is defined as an intentional maneuver involving an abrupt change in attitude, an abnormal attitude, or abnormal acceleration, not necessary for normal flight. Review of 14 CFR Part 91.307 indicates that unless each occupant wears an approved parachute, no pilot may execute any intentional maneuver exceeding a bank of 60 degrees relative to the horizon.
The airplane designer publishes a newsletter called RVator six times a year. According to company personnel, an issue about unsecured rod ends was first published in 1993 and republished as filler in the sixth issue of 2007. The issue contained three stories: one about in-flight separation of the elevator pushrod connecting front and rear sticks; one about disconnection of an aileron pushrod from the rod end during ground test; and one about in-flight separation of the elevator pushrod from the rear stick, after which the pilot baled out. Personnel reported that if the aileron pushrod assembly were to disconnect in flight, the roll rate would be half of normal, or about 180 degrees in 3 seconds.
Safety Board examination of RV-3 and RV-4 airplanes at the accident airport the day after the accident documented aileron pushrod assemblies. The RV-3 airplane had no rivets securing the pushrod to the rod end. The RV-4 airplane did have rivets securing the pushrod to the rod end.