BELMAR, NJ, USA
N121GP
Piper PA-46-310P
After takeoff, when the airplane was climbing through 12,000 feet, heavy black smoke appeared in the cockpit. The pilot declared an emergency, and successfully landed the airplane at a nearby airport. Post-flight inspection revealed that the left side turbocharger clamp had separated through the tensioning band, at the root of a spot weld. Subsequent microscopic examination in the area around the rim of the spot weld revealed a crystalline appearance. An analysis of a spot weld from the right turbocharger clamp revealed small recrystallized austenitic grains. The airplane's engine was installed in March 1991, and the turbochargers were replaced in June 1999. During the replacement, the turbocharger clamps were reused. The only requirement to change the turbocharger clamps was a mandatory replacement at engine overhaul.
On July 15, 1999, about 1355 Eastern Daylight Time, a Piper PA-46-310P, N121GP, suffered minor fire damage during an en route climb near Allaire Airport (BLM), Belmar, New Jersey. The pilot and two passengers were uninjured. Visual meteorological conditions prevailed at the time of the incident. An instrument flight rules flight plan had been filed for the instrument flight, between South Jersey Regional Airport (VAY), Mount Holly, New Jersey, and Boston, Massachusetts. The personal flight was conducted under 14 CFR Part 91. The pilot stated that the airplane had originally departed Brandywine Airport (N99), West Chester, Pennsylvania, and landed at South Jersey Regional. Two passengers then boarded the airplane for the flight to Boston. After takeoff, when the airplane was in a climb and passing 12,000 feet for 15,000 feet, heavy black smoke appeared in the cockpit. The pilot used his LORAN to locate the nearest suitable field, and declared an emergency. He then turned toward Allaire Airport and started an emergency descent. During the descent, he noticed that the hydraulic light was on and the hydraulic pressure was zero. Three to five minutes after initiating the emergency descent, the smoke started to dissipate. The pilot tried to move the prop control, but it wouldn't budge. He moved the throttle back 3 to 4 inches, then tried to move the prop again, but it still wouldn't budge. The throttle then also became difficult to move, but would move if the pilot yanked it a little at a time. The airplane arrived at Allaire, circled the field, and made an uneventful landing. Post-flight inspection of the airplane revealed that the left side turbocharger clamp from the Teledyne Continental TSIO-520-BE engine had failed. In addition, a hydraulic line had been burnt. Both turbocharger clamps were forwarded to the Safety Board Materials Laboratory for analysis. According to the Laboratory's factual report, each turbocharger clamp consisted of two semi-circular retainer segments and a circumferential tensioning band. The tensioning band was attached to the retainer segments by spot welds. The left turbocharger clamp had separated through the tensioning band. With the aid of a low power stereo microscope, the separation was observed to be at the root of a spot weld. The smaller piece of the separated band was cleaned ultrasonically in soapy water, then rinsed in acetone to remove loose deposits. "Subsequent examination with a binocular microscope showed the fracture face in the area around the rim of the spot weld had a crystalline appearance and was heat tinted dark blue." In addition: During a scanning electron microscope (SEM) review of the central portion of the fracture face on the smaller separated piece of the tensioning band, "the portion of the fracture that was found to be darkly discolored during binocular microscope examination disclosed intergranular fracture features and secondary intergranular cracking.... Outside of the intergranular fracture area, the fracture features consisted of ductile dimples.... X-ray dispersive spectroscopy (EDS), performed at the periphery of the fracture, generated spectra containing iron as a major peak with minor peaks of chromium and nickel, typical of austenitic type stainless steel. EDS spectra generated from the intergranular fracture region contained a major peak of chromium, a slightly lower peak of iron, and a minor peak of nickel. In addition to the peaks of these elements, all spectra contained small peaks of oxygen and lead, consistent with a combustion byproduct deposit. A section was cut perpendicular to the fracture face on the smaller separated piece of the band for metallographic examination. The microstructure of the polished and etched specimen in areas located both adjacent to and remote from the fracture surface contained carbide precipitates at the grain boundaries in what appeared 'original' cold worked microstructure. Also, numerous intergranular secondary cracks were noted in the area adjacent to the fracture." A note, regarding the manufacture of the band, included: "During manufacturing of the band, the band material is usually cold worked (rolled) to obtain the required tensile strength. The resultant microstructure consists of elongated grains and contains numerous slip lines." The right turbocharger clamp was not separated. However, of the four spot welds that attached the tensioning band to the retainer, three weld joints "contained cracks that by most part propagated around the weld rims. ...All cracks were confined to the tensioning band and did not penetrate to the retainer." A SEM view of the fracture surface in the area corresponding to the spot weld rim of an arbitrarily selected weld joint exhibited features "consistent with intergranular separation." In addition, "EDS analyses performed at several spots along the portion of the fracture that propagated along the weld rim produced spectra that contained chromium as the major peak. Also present in the spectra were an iron peak (second largest peak) and the peaks of nickel, oxygen, lead and bromine." A section was cut for metallographic examination. "The microstructure of the material in the area of the material located adjacent to the exterior surface was typical of the pre-welding cold worked condition. The microstructure in the portion of the heat affected zone (HAZ)...consisted of small recrystallized austenitic grains. Adjacent to the weld...in [a] portion of the HAZ...the microstructure consisted of enlarged recrystallized austenitic grains surrounded by chromium carbides. Metallographic examination of [one area] at higher magnifications showed the presence of numerous small intergranular cracks. Examination also showed that [one] crack...initiated in this portion of the HAZ." According to the airplane's maintenance logbooks, the engine was installed in the airplane in March 1991, and the turbochargers were replaced in June 1999. When the turbochargers were replaced, the turbocharger clamps were reused. According to information supplied by the engine manufacturer, the only requirement to change the turbocharger clamps was a mandatory replacement at engine overhaul, per Teledyne Continental Service Bulletin SB97-6. Visual inspection of the clamps was required at 100-hour intervals, per the manufacturer's engine overhaul manual. According to a representative from the engine manufacturer, the turbocharger clamps could have been received from one of two possible subcontractors. On March 7, 2000, the Safety Board's Materials Laboratory Report was provided to the engine manufacturer for an engineering review. As of June 7, 2000, no review response had been received.
The failure of the turbocharger clamp, resulting from improper welding settings during manufacture.
Source: NTSB Aviation Accident Database
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