NTSB Identification: ENG07IA034
14 CFR Part 91: General Aviation
Incident occurred Sunday, August 12, 2007 in Salt Lake City, UT
Probable Cause Approval Date: 03/23/2010
Aircraft: LEARJET, registration: N244F
Injuries: 2 Uninjured.
NTSB investigators traveled in support of this investigation and used data obtained from various sources to prepare this aircraft incident report.
The airplane experienced an in-flight fan blade separation in the left engine, a Pratt & Whitney Canada (PWC) PW305A turbofan, while the airplane was climbing through FL 380 shortly after takeoff from Salt Lake City (SLC), Utah. The airplane returned to SLC for an overweight, single-engine landing without further incident. Examination of the engine revealed that two fan blades were fractured transversely across the airfoil adjacent to the blade root platform. Metallurgical examination of the fan blades determined that one fan blade had separated from a fatigue fracture and the other separated from overload, although the fracture had coincided with a preexisting fatigue crack. A fluorescent penetrant examination of the left engine's remaining fan blades revealed that several blades had crack indications. A dimensional inspection of the cracked fan blades revealed that they were under the minimum thickness in a highly stressed area of the airfoil. The investigation determined that the fan blades were too thin due to an improper forging die setup when the blades were manufactured. At the time the fan blades were made, PWC did not require a dimensional inspection of the fan blade airfoils.
The National Transportation Safety Board determines the probable cause(s) of this incident to be: The fatigue fracture of the fan blade due to the blade vendor's improper setup of the forging dies, which resulted in fan blades with airfoils that were below the minimum thickness in the highest stressed area of the airfoil and resulted in operating stresses that exceeded the material's capability. Contributing to the incident was the engine manufacturer's lack of a dimensional inspection of the fan blade's airfoil. Full narrative available
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