ERA16FA185

A preexisting stress rupture that initiated at a spot weld in the turbocharger v-band exhaust clamp, which resulted in the failure of the clamp and separation of the exhaust tailpipe, an in-flight fire, and subsequent impact with terrain.

The airline transport pilot was taking off in the turbocharged reciprocating engine-equipped airplane for a personal flight. One witness reported seeing something fall from the airplane as it departed. Shortly after departure, the pilot notified air traffic control of smoke in the cockpit. The airplane then made a left, westbound turn back toward the airport, about 500ft above the ground and then it turned back toward the approach end of the departure runway while descending. Two witnesses also reported seeing fire and smoke coming from the bottom, left side of the airplane before it impacted terrain. After the accident, airport personnel found the exhaust tailpipe and fractured v-band coupling on the runway. A support clamp, which was intended to support the exhaust tailpipe, was not found. Examination of the v-band coupling revealed stress rupture features at the edge of a spot weld that attached the outer band to the retainer, which led to the v-band fracturing, the exhaust tailpipe separating from the airplane, and an in-flight fire. Review of the maintenance records did not reveal when the v-band coupling was installed or last inspected. There is a longstanding history of accidents and incidents resulting from v-band coupling failures on both fixed-wing aircraft and rotorcraft. Although before the accident the Federal Aviation Administration (FAA) had issued six v-band-specific airworthiness directives (AD) and other guidance materials and recommendations related to v-band failures, none of them were specific to the accident airplane make and model. Subsequent to the accident, the FAA published a notice of proposed rulemaking to obtain public feedback regarding a proposed AD that would require a repetitive annual inspection of, and would impose a 500-hour life limit on, the exhaust tailpipe v-band coupling on the accident aircraft make and model.

The recovered exhaust tailpipe and v-band coupling were forwarded to the National Transportation Safety Board's Materials Laboratory, Washington, DC, for further examination. The v-band coupling consisted of a flat band with fastening hardware and two inner flange retainers located on flanges on the turbocharger housing and the exhaust tailpipe. Each flange retainer was spot welded to the inner surface of the band at two locations. Further examination of the coupling revealed that the fracture occurred at the edge of a spot weld attaching the outer band to the retainer. The fracture occurred due to a stress rupture initiating at the edge of a spot weld between the band and the retainer and extending across about 60% of the width of the band. Examination with a scanning electron microscopy further revealed that much of the fracture surface was oxidized with crack propagation at the grain boundaries, consistent with the existence of a preexisting crack. Cracks and local deformation were also observed at the edge of another spot weld on the coupling. No part number or manufacturer identification marks were found on the on the v-band coupling. Because there are multiple manufacturers of v-band clamps/couplings, the manufacturer and installation date of the accident airplane's v-band coupling could not be determined. A v-band coupling is a common way of attaching portions of an exhaust system and are widely used throughout the aviation industry on reciprocating turbocharged engines. V-band couplings are exposed to extremely high exhaust temperatures and heat cycles. High temperatures and corrosive conditions can lead to cracks and failures of the couplings, which result in hot exhaust gases escaping the exhaust system and subsequently can result in smoke in the cockpit, in-flight fires, and fatal accidents. Since the mid-70s, v-band coupling failures have resulted in a significant number of nonfatal and fatal incidents and accidents involving both fixed-wing aircraft and rotorcraft. Since 1974, NTSB accident and incident investigations have led to the development and issuance of at least seven NTSB safety recommendations concerning exhaust systems and/or exhaust v-band coupling/clamps. In response, the FAA has issued 20 aircraft-model-specific airworthiness directives (AD) in which v-band coupling/clamps were included, six of which were v-band specific. In 1979, the FAA issued the first AD that was aircraft make and model specific. The AD required the inspection of, and provided replacement intervals for, v-band couplings. However, there are many airplanes and helicopters, including the accident airplane, equipped with v-band couplings susceptible to fractures and failure that were not covered by the AD. In 2001, the FAA issued AD 2001-08-08 for Beech A36 airplanes with the Tornado Alley Turbo conversion; however, the accident airplane was not equipped with this conversion; therefore, it was exempt from the AD. The FAA has also provided guidance and recommendations in at least 10 special airworthiness information bulletins (SAIB), published numerous advisory circular (AC) 43-16A Maintenance Alert articles, and updated existing AC guidance. Many of these products result from specific accidents and only addressed a specific accident airframe or engine. In 2013, the FAA issued an SAIB to inform owners, operators, and mechanics about the potential for in-flight fires due to the failure of the exhaust system v-band on turbocharged engines. The SAIB urged pilots to include the exhaust system in preflight inspections, establish a replacement schedule of 400 hours of time in service, adhere to inspection criteria from the manufacturers, and use new FAA-approved parts and appropriate maintenance documentation for replacement of v-band couplings. The General Aviation Joint Steering Committee (GA-JSC) developed a System Component Failures – Power Plant (SCF-PP) working group to examine general aviation accident causes. The SCF-PP working group reviewed 70 randomly selected fatal accidents that occurred between 2001 and 2010 and found that three of the selected cases resulted from v-band coupling/clamp failures. Due to the findings, the SCF-PP working group asked the GA-JSC to examine the feasibility of implementing fleetwide inspection requirements and life-limits for v-band coupling/clamps on all turbocharged, reciprocating engine-powered aircraft not already covered by an existing AD, regardless of make or model. The accident in Tupelo occurred shortly after the completion the SCF-PP working group effort. On November 8, 2017, the FAA published a notice of proposed rulemaking (NPRM) to obtain public feedback regarding a proposed AD that would require a repetitive annual inspection of, and would impose a 500-hour life limit on, the exhaust tailpipe v-band coupling. The NPRM was specifically written for the accident aircraft make and model and included other turbocharged Beech Bonanza models. Industry has also taken action to raise awareness of the concerns associated with v-band coupling/clamp failures by publishing articles in various trade magazines and user group newsletters, issuing installation guidance, and clarifying installation requirements for v-band coupling/clamps. The 0847 weather conditions reported at TUP, located about 2 nautical miles south of the accident site, included wind from 130° at 9 knots, 10 statute miles visibility, temperature 19°C, dew point 5°C, and altimeter setting of 30.17 inches of mercury. The Mississippi State Medical Examiner's Office, Pearl, Mississippi, performed autopsies on all of the airplane's the occupants. The autopsy reports listed the cause of death for all occupants as "blunt force injuries." The FAA's Bioaeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma, performed toxicological testing on the pilot. No cyanide, ethanol, or drugs were detected in the samples submitted for testing. Toxicology testing indicated 3% carbon monoxide in the blood. The pilot held an airline transport pilot certificate and a flight instructor certificate with airplane single-engine land, multiengine land, and instrument airplane ratings. His most recent Federal Aviation Administration (FAA) third-class medical certificate was issued on October 24, 2014, with the limitation that he "must wear lenses for distant and have glasses for near vision." At the time of his last medical evaluation, the pilot reported 5,675 total flight hours. The pilot's logbooks were not available for review, and his total flight experience at the time of the accident could not be determined. The six-seat, low-wing, retractable tricycle-gear airplane was manufactured in 1980. It was powered by a Continental TSIO-520-UB series, 300-horsepower engine and was equipped with a McCauley three-blade, constant-speed propeller. A review of maintenance records revealed that the airplane's most recent annual inspection was completed on April 19, 2016. At that time, the airplane had accumulated 2,037 total flight hours. At the time of the annual inspection, the engine had accumulated 242.1 hours since an overhaul completed on December 26, 2012. The exhaust system was not specifically mentioned in the logbook entries for the overhaul or engine reinstallation. The airplane accumulated 58.6 hours over the 12 months that preceded the April 19, 2016 inspection. The exhaust system, v-band coupling, and exhaust tailpipe support clamp were not specifically discussed in the logbook entries for the annual inspection; therefore, it could not be determined when the coupling and support clamp were last inspected. Due to thermal damage to the cockpit, the airframe and engine total time could not be determined. The Continental Aircraft Engine Maintenance Manual required a visual inspection at every 100-hour and annual inspection to "Inspect the physical integrity of the turbocharger and exhaust system. Inspect multi-segment v-