NTSB Identification: SEA07IA201
14 CFR Part 91: General Aviation
Incident occurred Sunday, July 15, 2007 in Reno, NV
Probable Cause Approval Date: 01/14/2009
Aircraft: Cirrus Design Corp. SR22, registration: N254SR
Injuries: 2 Uninjured.
NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.
During cruise flight at 17,000 feet mean sea level, the left turbocharger failed, resulting in a partial engine power loss. The pilot declared an emergency and executed an uneventful landing at an alternate airport. Examination of the turbocharger revealed the turbine wheel was separated from the shaft. Three prior incidents involving similar failures of this part number turbocharger had occurred in May 2007. Examination of the failed turbochargers from all four incidents revealed that all of the units displayed the same discrepancy: the compressor wheel backface perpendicularity to the bore exceeded the maximum permissible value. The source of the perpendicularity error was traced to a change, made in March 2007, to the machining process for the compressor wheel. The change involved a switch from a two-machine process to a three-machine process. This production change was made without formal documentation or coordination with other functional areas; no formal first-article inspection for the new process was performed. In April 2007, the machine shop returned to the original two-machine process. The compressor wheels manufactured during the time that the three-machine process was in use were installed in turbochargers produced from March 20 to April 20, 2007, including the four turbochargers involved in the subject incident and the three May 2007 incidents. The manufacturer issued service bulletins in July 2007 identifying the affected turbochargers by serial number and mandating their replacement. In August 2007, the Federal Aviation Administration issued an airworthiness directive requiring compliance with the service bulletins.
The National Transportation Safety Board determines the probable cause(s) of this incident to be: The failure of the left turbocharger as a result of a production defect in the unit's compressor due to a machining process change by the manufacturer that was made without formal documentation or substantiation. Full narrative available
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