Incident Summary
Shortly after takeoff, following gear retraction, the aircrew heard a loud noise and observed that the #2 engine had failed at approximately 150 feet above ground level. They secured the engine, dumped fuel, and landed without further incident.
Examination Findings
An examination of the failed engine revealed that the combustion chamber outer case, part number 616315, had failed due to high stress, low-cycle fatigue. The failure originated at a 4.6-inch crack located at the rear drain boss to case weld.
Inspection and Detection Issues
At the last shop inspection, a suspected crack was visually observed in that area. The case was prepared for non-destructive testing by grit blasting it with aluminum oxide beads to strip off the nickel-cadmium plating. However, the non-destructive testing did not reveal a crack. Consequently, the case was recoated with nickel-cadmium and returned to service.
After the failure, examination of the fracture area revealed the presence of nickel and cadmium (0.5 to 0.75 inch, centered on the fracture origin area). Evidence indicated that the grit blasting performed prior to non-destructive testing had mechanically closed the previous crack, thereby preventing its detection.
Remedial Action
In response, the operator revised the shop procedure to use a shell blasting method instead.