LAPEER, MI, USA
N7033G
Corey CIRRUS VK-30
According to witnesses, the accident pilot reported on Unicom that his 'flap bracket had broken.' A pilot who was on the ground near the accident site reported that he observed a 'violent flutter' on the right wing. Examination of the right flap revealed the inboard flap push rod was fractured at the end cap. The push rod welds exhibited 'porosity and secondary cracking indicative of poor welding techniques.' The inboard cruise flap push rod 'exhibited a thumbnail crack, which may have indicated failure by high stress, low cycle fatigue.' The outboard cruise flap hinge was fractured. Examination revealed the hinge was constructed entirely of composite material. The kit manufacturers drawings specify an aluminum core for the hinge. Differential scanning calorimetric analysis of the composite cruise flap skin revealed the vinyl ester matrix material was 'not fully cured.'
HISTORY OF FLIGHT On June 3, 1996, at 1455 eastern daylight time, an experimental Cirrus VK-30 airplane, N7033G, was destroyed when it impacted terrain during an emergency landing attempt near Lapeer, Michigan. Witnesses reported that the pilot reported that he had a "broken flap bracket" on unicom. Eyewitnesses observed the right flap "fluttering" and the engine "screaming under no load" prior to the accident. The solo private pilot sustained fatal injuries. The personal flight originated about 1430 and was conducted under 14 CFR Part 91. A flight plan was not filed for the local flight and visual meteorological conditions prevailed. Witnesses at the Lapeer DuPont Airport reported that the pilot onloaded 20 gallons of aviation fuel about 1415. A local instructor reported that there were thunderstorms west of the airport and the accident pilot "commented he would stay close to the airport." The Assistant Airport Manager reported that there was "nothing unusual" about the local weather at the time and he observed the accident airplane do a "normal" takeoff and climb. According to witnesses, about 1440, the accident pilot reported on unicom that he "had a problem" and was "probably going in." A certified flight instructor (CFI), who was flying in the local traffic pattern, queried the accident pilot about his location. The accident pilot responded that he was "north of the airport." The CFI "told him to stay calm and fly the airplane." The accident pilot responded that his "flap bracket had broken." Witnesses reported that the accident pilot "had his transmit button held down." The accident pilot said "here I go." A few seconds later witnesses heard the sound of the airplane impact on the radio. A pilot who was on the ground near the accident site reported that he first observed the airplane at an altitude of 200 feet above the ground. He estimated it was traveling at 140 to 150 miles per hour. The landing gear was down. He observed a "violent flutter" on the right wing. The engine sound was "extremely loud... screaming... like the pilot was working the throttle... engine would idle back and accelerate almost like there was no load on the engine." He reported that the wings were level when the airplane traveled out of his line of sight. Another witness, who was at his house near the accident site, reported that he heard the accident airplane. He thought the "engine was cutting out." He saw the airplane "go high, then down." He reported that he observed the right wing flap fluttering. WRECKAGE AND IMPACT INFORMATION The accident site was a small, grassy clearing located approximately 1/4 mile south of the residence located at 2334 Scott Road. The clearing was located in a wooded area and was surrounded by trees. The initial on-scene investigation was conducted by a Federal Aviation Administration (FAA) Airworthiness Inspector. He reported that the wreckage path was oriented on a southerly heading. The first item in the wreckage path was a small ground scar immediately followed by a large impact crater. Green glass fragments and an aileron counter weight were located in the first ground scar. Several ground scars led to the main wreckage which was located about 300 feet south. The wreckage and surrounding vegetation were severely burned. The fuselage structure was fragmented into multiple small, charred fragments and sooty, fibrous dust. The composite propeller drive shaft was severely burned. The remnant fiber of the shaft exhibited continuity from the propeller to the elastimeric coupling. The elastimeric coupling was melted. All three blades of the composite, wood propeller were fractured near the root. The wings were fragmented into multiple pieces. Extension of the landing gear actuators corresponded to the gear up position for all three actuators. Extension of the flap actuators corresponded to a flap position of approximately 75 percent extended. Primary flight controls and engine control continuity revealed no evidence of preimpact malfunction. The engine, right flap, and cruise flap assembly were retained for further investigation. MEDICAL AND PATHOLOGICAL INFORMATION An autopsy of the pilot was performed by the Lapeer County Medical Examiner's Office, 1575 Suncrest Drive, Lapeer, Michigan 48446, on June 6, 1996. Toxicological testing performed by the Federal Aviation Administration was negative for all tests conducted except for hydrochlorothiazide detected in the blood specimen. Hydrochlorothiazide is a common diuretic used for the control of high blood pressure and is approved by the FAA. TESTS AND RESEARCH The engine was examined at Teledyne Continental Motors, in Mobile, Alabama, on July 19, 1996. The engine exhibited severe fire damage, but "did not exhibit any condition that would have caused an operational problem." The right flap assembly was examined at the Wright Laboratory, Wright-Patterson Air Force Base, Ohio. The flap exhibited a transverse fracture inboard of the center flap track. Detailed examination of the fracture revealed some burning of the material and evidence of "a bending fracture." The inboard flap push rod was fractured at the end cap. The rod exhibited no bending. Fractographic examination revealed "cleavage due to overload." Magnetic particle inspection of the intact end of the push rod revealed a crack around the circumference of the weld. A cross section of the joint "revealed porosity and secondary cracking indicative of poor welding techniques." The inboard flap track was destroyed by fire. The rollers in the center flap track were seized. The rollers in the outboard flap track traveled freely. The flap end caps were separated from the flap at both the inboard and outboard tracks. Examination of the separations revealed that most of the rivets were pulled through the surrounding material in an aft, upward direction. The outboard cruise flap push rod was separated at the weld joint and exhibited evidence of "tensile overload." The inboard push rod "exhibited a thumbnail crack, which may have indicated failure by high stress, low cycle fatigue." No fatigue striations were found on the fracture surface. The outboard cruise flap hinge was fractured. Examination revealed the hinge was constructed entirely of composite material. Cirrus Design Corporation Drawings specify an aluminum core for the hinge. The fracture was fire damaged and "the reason for the fracture could not be determined." "Examination of the inboard fracture at the push rod attachment of the bell crank system revealed bending... cracking...large ductile dimples, indicative of tensile overload." The inboard section of the upper skin and the lower skin of the cruise flap was not located. Fractographic examination of the fractures revealed evidence of "bending and tearing" in the vicinity of the cutout for the control rod. Visual examination revealed several transverse cracks in the foam stiffener and several 45 degree cracks on the inboard portion of the skin. Microscopic examination of the underside of the upper skin revealed "river patterns indicative of mode I type overload fracture or peeling." Crack growth direction indicated that separation of the upper to lower skin occurred in the inboard, aft direction. "The presence of river patterns and fractured adhesive on the bonded surface indicates the upper skin was originally well bonded to the lower skin at the leading and trailing edges." Differential scanning calorimetric analysis of the composite skin revealed the vinyl ester matrix material was "not fully cured" ADDITIONAL INFORMATION Parties to the investigation were the Federal Aviation Administration, Flight Standards District Office, Belleville, Michigan, and Cirrus Design, Corporation. Following the on-scene investigation, all wreckage except for the engine and right flap assembly were released to the Manager of the Lapeer DuPont Airport. Following laboratory examination, the engine was shipped to a representative of the pilot's wife. The flap assembly was destructively tested.
incomplete cure of the bonding material in the cruise flap, improper material in the cruise flap hinge, and improper welding of the cruise flap push rod end caps. Factors were delamination of the cruise flap, partial failure of the cruise flap hinge, and fatigue failure of the outboard cruise flap push rod.
Source: NTSB Aviation Accident Database
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