What happened
The flight crew experienced an in-flight failure of the number two engine shortly after initiating takeoff. The immediate mechanical cause was identified as the rupture of the engine's combustion outer case.
The investigation
A detailed metallurgical examination was conducted on the failed component to determine the root cause of the structural failure. The analysis revealed that a half-inch crack was already present in the combustion outer case prior to its last overhaul, which occurred 16 flight cycles before the incident.
Further testing determined that the nickel and cadmium plating applied during the overhaul process did not meet the required thickness specifications. This improper plating resulted in cadmium embrittlement of the base material within the case. The embrittled material lacked the necessary structural integrity to withstand operational stresses, leading directly to the catastrophic rupture.
Findings
The investigation concluded that the engine failure was caused by cadmium embrittlement of the combustion outer case. This metallurgical degradation was a direct result of improper plating thickness during maintenance and the presence of a pre-existing crack in the component.