History of Flight
On May 16, 2016, at about 0835 central daylight time, a Beech A36TC, registration N60RW, impacted terrain in Tupelo, Mississippi. The airline transport pilot and three passengers sustained fatal injuries, and the airplane was destroyed by postcrash fire. The flight was operating as a personal flight under Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed at the airport, and an instrument flight rules flight plan was filed for the flight that originated at Tupelo Regional Airport (TUP) about 0830, destined for Charlottesville-Albemarle Airport (CHO), Charlottesville, Virginia.
According to air traffic control recordings, shortly after departing runway 36, the pilot advised the tower controller that there was smoke in the cockpit and that he needed to return to the airport. One witness reported seeing something fall from the airplane as it departed. Several witnesses reported that the airplane made a left, westbound turn toward the airport at an altitude of about 500–1,000 feet above ground and then turned back toward the approach end of runway 18 while descending. Two witnesses reported seeing the airplane about 50 feet above them with smoke and flames coming from the bottom, left side of the airplane before it impacted terrain. Shortly after the accident, TUP personnel conducted a sweep of the runway and found the exhaust tailpipe and a fractured v-band coupling.
Personnel Information
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.
Aircraft Information
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, and 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 preceding the annual 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-band clamp spot welds (or rivets) for cracks or physical damage. Inspect the corner radii of the clamp inner segments for cracks with a flashlight and inspection mirror. Inspect the v-band clamp outer band for flatness, especially within two inches of spot-weld tabs that retain the T-bold fastener variance must be less than 0.062 in." The turbocharger and exhaust system inspection portion of the 100-hour inspection criteria stated, "Verify 100% inner and outer band segment contact." The instructions were accompanied by a diagram of the required v-band clamp inspection and instructions for cleaning the v-band clamp. The preflight checklist did not include an inspection of the exhaust system.
Wreckage and Impact Information
The wreckage, mostly consumed by fire, was located on flat terrain with trees nearby. Tree cuts began about 50 feet above the terrain and descended at about a 20° angle for about 165 feet along a magnetic heading of 110°. All flight control surfaces were accounted for, and flight control continuity was confirmed from the cockpit to their respective control inputs. The outboard portion of the right wing was found about 80 feet past the initial tree strike; it was separated from the airframe and heavily burned. The right aileron remained attached, but the right flap was separated. The left wing remained attached at the forward spar but sustained extensive fire damage.
One of the three propeller blades exhibited S-bending, leading edge gouging, and chordwise scratches. The second blade exhibited tip curling and aft bending. The third blade displayed aft bending and minor chordwise scratches.
The engine exhaust pipe was missing from the exhaust side of the turbocharger. Subsequent examination of the engine at a recovery facility did not reveal any other preexisting mechanical anomalies that would have precluded normal operation. Thumb compression was obtained on all cylinders, and continuity was confirmed throughout the drive train. The magnetos were removed and rotated, and a spark was observed at each of their respective terminal leads.
The exhaust tailpipe was separated at the exhaust flange of the turbocharger. The exhaust tailpipe flange was crushed, consistent with impacting the runway. The separated v-band coupling, which attaches the tailpipe to the turbocharger, was attached at the ends by a bolt and safety wire but was fractured through its band. The tailpipe support clamp, which holds the tailpipe to a bracket attached to the engine, was missing and not located in the wreckage or on the runway.
Additional Information
A v-band coupling is a common means of attaching exhaust system components and is widely used on reciprocating turbocharged engines. V-band couplings are exposed to high exhaust temperatures and heat cycles, which can lead to cracks and failures. Such failures can result in hot exhaust gases escaping, leading to smoke in the cockpit, in-flight fires, and accidents.
Since the mid-1970s, v-band coupling failures have been associated with numerous incidents and accidents involving fixed-wing aircraft and rotorcraft. The NTSB has issued at least seven safety recommendations concerning exhaust systems and v-band couplings since 1974. In response, the FAA has issued 20 aircraft-model-specific airworthiness directives (ADs) involving v-band couplings, six of which were v-band specific. The first AD was issued in 1979, requiring inspection and replacement intervals for v-band couplings on certain models. However, many airplanes and helicopters, including the accident airplane, were not covered by that AD. In 2001, the FAA issued AD 2001-08-08 for Beech A36 airplanes with the Tornado Alley Turbo conversion; the accident airplane was not equipped with this conversion and therefore was exempt.
The FAA has also provided guidance in at least 10 special airworthiness information bulletins (SAIBs), numerous advisory circular (AC) 43-16A articles, and updated AC guidance. In 2013, the FAA issued an SAIB regarding potential in-flight fires from exhaust system v-band failures on turbocharged engines, urging pilots to include the exhaust system in preflight inspections and establish a replacement schedule of 400 hours.
The General Aviation Joint Steering Committee (GA-JSC) formed a System Component Failures – Power Plant (SCF-PP) working group, which reviewed 70 randomly selected fatal accidents between 2001 and 2010 and found three cases resulting from v-band coupling failures. The working group requested examination of fleetwide inspection requirements and life-limits for v-band couplings on turbocharged reciprocating engine aircraft not already covered by an AD. The Tupelo accident occurred shortly after the completion of that effort.
On November 8, 2017, the FAA published a notice of proposed rulemaking (NPRM) to require repetitive annual inspection and a 500-hour life limit on exhaust tailpipe v-band couplings for the accident aircraft make and model and other turbocharged Beech Bonanza models.
Industry has also published articles, installation guidance, and clarified installation requirements for v-band couplings to raise awareness of failure concerns.
Medical and Pathological Information
The Mississippi State Medical Examiner's Office performed autopsies on all occupants. The cause of death for all occupants was listed as "blunt force injuries." The FAA's Bioaeronautical Sciences Research Laboratory performed toxicological testing on the pilot. No cyanide, ethanol, or drugs were detected. Toxicology testing indicated 3% carbon monoxide in the blood.
Tests and Research
The recovered exhaust tailpipe and v-band coupling were forwarded to the NTSB Materials Laboratory for examination. The v-band coupling consisted of a flat band with fastening hardware and two inner flange retainers spot welded to the inner surface of the band at two locations. Examination revealed that the fracture occurred at the edge of a spot weld attaching the outer band to the retainer, due to a stress rupture initiating at that edge and extending across about 60% of the band width. Scanning electron microscopy showed much of the fracture surface was oxidized with crack propagation at grain boundaries, consistent with 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 v-band coupling, so its manufacturer and installation date could not be determined.