ERA18FA221

The in-flight fracture of a stainless steel bolt that was used to secure the upper and lower wing cables to the outer attach point at the leading edge spar of the right wing due to stress corrosion cracking, which caused the right wing to fail and precluded controlled flight. Contributing to the bolt failure was the installation of a bolt that did not conform with the company's specification.

The private pilot and a passenger departed on a local flight and returned for landing about 15 minutes later. While the airplane was on final approach at an altitude between 100 and 200 ft, several witnesses heard a loud sound, and one of the witnesses saw the right wing fold and the airplane enter a steep descent. The airplane subsequently impacted terrain in a field near the airport. A witnesses reported observing the airframe parachute system deploy. The inspection of the components of the airframe ballistic parachute system indicated that the system had likely deployed just before or at the time of impact. Deployment of the parachute system at that low altitude would have been insufficient to adequately arrest the airplane's descent prior to impact. A stainless steel bolt secured the upper and lower wing cables to the outer leading edge spar of the right wing. Examination of the bolt showed that it fractured during flight due to stress corrosion cracking that extended across about 95% of the cross-section area of the bolt shank. The bolt failure allowed the leading edge spar to rotate upward relative to the trailing edge spar and fracture at the inboard cable attach point, precluding controlled flight. The stainless-steel material used for the wing cable attachment bolt was susceptible to stress corrosion cracking when exposed to a chloride-containing environment (such as the ocean). The airplane was previously equipped with floats, and was likely operated as an amphibious airplane at some point before the pilot purchased it. In addition, the installed bolt was a different material than the AN5-30A bolt specified in the Quicksilver Assembly, Maintenance, and Parts Manual for securing the outer upper and lower wing cables to the leading edge spar of the right wing. The material of the bolt recommended in the manual would be generally resistant to stress corrosion cracking as a result of a chloride-containing environment. The maintenance records did not indicate when the stainless steel bolt was installed. Evidence of stress corrosion cracking might not be apparent during visual inspections of the bolted joint. Also, the location of the stress corrosion cracking on the bolt would likely not have been detected during a condition inspection with the bolted joint in place. Further, the assembly, maintenance, and parts manual did not provide for a specific inspection of the bolt that secured the upper and lower wing cables to the outboard leading edge spar. However, the manual indicated that the security of all bolts should be checked every 50 hours. Although the pilot was taking a medication that could impair his ability to perform tasks requiring judgment or motor and cognitive skills, his use of the medication did not contribute to the accident.

The pilot held a private pilot certificate with an airplane single-engine land rating and a third-class medical certificate issued on October 18, 2017, with the limitation "must wear corrective lenses for near and distant vision." On the medical certificate application, the pilot reported 1,200 hours of total flight experience. The pilot also held a repairman certificate for light sport aircraft, with a limitation for the inspection of the accident airplane. The Office of the Chief Medical Examiner, State of Maryland, Baltimore, Maryland, performed an autopsy on the pilot. His cause of death was multiple injuries. Toxicology testing performed at the FAA Forensic Sciences Laboratory detected acetaminophen in the pilot's urine specimens and bupropion (and its metabolite hydroxybupropion), tamsulosin, and diltazem in the pilot's urine and cavity blood specimens. No carbon monoxide or ethanol were detected in the pilot's specimens. Bupropion is an antidepressant marketed with the name Wellbutrin and is the active drug in Zyban, often marketed to help with smoking cessation. Bupropion can cause various neuropsychiatric symptoms and seizures, and prescribers are advised to counsel patients that the use of the drug could "impair their ability to perform tasks requiring judgment or motor and cognitive skills." Tamsulosin is prescription medication used to treat symptoms from an enlarged prostate, and diltiazem is a prescription medication used to treat blood pressure. Acetaminophen is an over-the-counter analgesic often marketed with the name Tylenol. These three drugs are not considered to be impairing. The high-wing, two-seat, tricycle gear airplane was built in 2006 and purchased by the pilot and his wife during August 2010. It was powered by a 65-horsepower Rotax 582 UL DCDI engine and was equipped with a Warp Drive four-bladed 62-inch composite adjustable propeller. The airplane was also equipped with a BRS-5 model UL2 ballistic airframe parachute that was mounted to the main axle tube behind the right seat. The wing structure consisted of leading and trailing edge spars separated by a diagonal tube at the inboard end and four spanwise tubes. Eight support cables were attached to each wing at four attachment locations. On the wing, the cables were attached to the leading and trailing edge spars at the locations of the inboard and outboard middle chordwise tubes. According to the Quicksilver Assembly, Maintenance, and Parts Manual, an AN5-30A bolt is one of the parts used to secure the upper and lower wing cables to the outboard attach point at the leading edge wing spar. The head of the bolt pointed downward, and the lower leading edge outboard cable was attached to the lower surface of the leading edge spar by the bolt, and the anti-drag cable, bellcrank strut cable, and upper leading edge outboard cables were attached to the upper surface of the leading edge spar. The section of the manual titled Construction Notes specifies that AN quality bolts are used throughout the airplane for structural integrity and indicates "NEVER USE SUBSTITUTES!" Although the manual did not provide a specific inspection interval for the bolt that secured the upper and lower cables to the outboard leading edge spar, the manual indicated that the security of all bolts and nuts should be checked every 50 hours. The available maintenance records contained entries from January 6, 2010, to May 9, 2013. Review of the records revealed that entries dated January 6 and 7, 2010, documented the condition inspection of the airplane for the issuance of a Light Sport Aircraft Airworthiness Certificate. An entry dated July 21, 2010, indicated the removal of floats and amphibious landing gear and the installation of standard Quicksilver wheels and brakes. At that time, the airplane had accumulated 81 hours. None of the remaining entries specified the removal and replacement of the bolt that secured the wing cables to the outboard attach point at the right wing leading edge spar. On August 18, 2018, about 1040 eastern daylight time, a Quicksilver MXL II Sport light sport airplane, N105SE, was substantially damaged when it impacted a field near Baugher's Orchard Airport (07MD), Westminster, Maryland. The private pilot and passenger were fatally injured. The airplane was owned and operated by the pilot as a Title 14 Code of Federal Regulations Part 91 personal flight. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight, which originated about 1025 from 07MD. Witnesses at the airport reported that the flight departed normally, flew to the north, before returning and entering the final approach for landing. One witness (the 07MD manager) reported that, when the airplane was about ¼ to ½ mile from the runway, a loud "bang" was heard. One witness reported the sound as a "high pitch crack of something under stress." The 07MD manager provided the account of a witness who wanted to remain anonymous. This witness was looking directly at the accident airplane during its landing approach. The witness indicated that the loud "bang" was followed by the "upward folding" of the right wing, after which the airplane rolled to the right and descended. Another witness stated that the wing "broke" when the airplane was at an estimated altitude of 100 to 200 ft. The 07MD manager observed the airplane descending "straight down" while rotating to the right and noted that the airframe parachute "blew" just before impact. Two witnesses who were located about 2,100 ft south-southeast of the accident site reported hearing a sound similar to a sputtering engine followed by a "bang" sound. One of the witnesses reported that the airplane then began descending, and the other witness reported seeing white/gray dust. This witness could not discern the airplane's altitude when she saw the dust. The airplane crashed into a field located about 1,500 ft and 003° from the approach end of the runway. The cockpit was inverted, and the main wreckage was located along a magnetic heading of 124°. All airplane components were located within or near the main wreckage. There was no evidence of fire on any airplane component, but black soot had discolored the sheath of a cable attached to the BRS rocket near the rocket exhaust. The engine had separated and was found near the mount location on the airframe. The right wing was beneath the inverted empennage, and the outer section of the left wing was laying over the top of the wreckage. A section of wing cable with a fractured attach bolt was found resting on the engine between the propeller and gearbox. The head of the bolt was not located. Flight control continuity in the roll and yaw axes was confirmed from the respective cockpit control to the respective control surface. Control continuity in the pitch axis was confirmed through breaks in the elevator control system that were consistent with overload and impact damage. The elevator trim tab was in the tab trailing-edge-down position. Multiple tailboom tubes were fractured in a manner consistent with bending overload. On-scene examination of the left wing revealed that the leading edge spar was fractured about 61 3/8 inches from the root tube attachment and that the trailing edge spar was fractured about 62 inches outboard of the structural attach point. The lower forward inboard wing cable was fractured about 11 inches from the attach point on the tube, and the upper aft inboard wing cable was fractured about 12 inches from the king post. All other cables remained attached to their respective attach points on the wing and structure. Examination of the left wing by the National Transportation Safety Board (NTSB) Materials Laboratory found that the fracture surfaces of both the leading and trailing edge spars were on slant angles and had a matte gray color consistent with ductile overstress fracture, which was consistent with aft bending loads on the leading