Incident Details
The airplane experienced an uncontained failure of the left engine, resulting in minor damage to the aircraft. Examination of the engine revealed that the fan spinner was completely missing, and the forward fan blade retainer had lost a 90-degree section of its bolt flange. Several fragments of the fan spinner were found within the engine cowl.
Examination Findings
The National Transportation Safety Board (NTSB) inspected the fan blade forward retaining ring and found features indicative of overstress failure. The fracture originated on the forward face adjacent to a linear impression. The length and location of this impression corresponded to a bolt lug on the aft side of the spinner. The linear impression showed evidence of fretting damage. The inside radius between the retaining ring's raised lip and its flange was within the manufacturer's specified range. However, the spinner's bolt lugs had a sharp outside corner where they interfaced with the retaining ring radius. The forging drawing for the spinner did not specify a radius, but a manufacturer representative indicated that an engineering drawing required an edge break with a radius between 0.005 and 0.020 inches on exterior corners. The combination of the retaining ring radius and the sharp edge on the spinner created interference during assembly.
Further examination by the manufacturer revealed high-cycle fatigue on both the spinner and the fan blade retaining ring. Three-dimensional finite element analysis predicted a reduced low-cycle fatigue life for these components.
Manufacturer Response
As a result of the investigation, the manufacturer initiated a one-time, on-wing eddy current inspection of all one-piece fan spinners, to be completed within 18 months or 2,000 operating hours. Additionally, the manufacturer started a redesign of the fan spinner and stated that all one-piece fan spinners would be removed from service by the end of 2010.