Incident
The airplane was climbing through Flight Level 380 shortly after takeoff from Salt Lake City (SLC), Utah, when the left engine, a Pratt & Whitney Canada PW305A turbofan, experienced an in-flight fan blade separation. The crew returned to SLC and performed an overweight, single-engine landing without further incident.
Investigation
Examination of the left engine revealed that two fan blades were fractured transversely across the airfoil adjacent to the blade root platform. Metallurgical analysis determined that one blade had separated from a fatigue fracture, while the other separated from overload, with the fracture coinciding with a preexisting fatigue crack.
A fluorescent penetrant inspection of the remaining fan blades found several blades with crack indications. Dimensional inspection of the cracked blades showed that they were under the minimum thickness in a highly stressed area of the airfoil.
Findings
The investigation determined that the fan blades were too thin due to an improper forging die setup during manufacturing. At the time the blades were produced, Pratt & Whitney Canada did not require a dimensional inspection of the fan blade airfoils.