Accident Summary - continued

It is important to note that although the flight crew was experimenting with the aircraft systems and not following an approved procedure, the root cause of the failure was not the improper flight crew actions in the cockpit, but a design problem with the engine.

The maximum speed of the fan rotor on the No. 3 engine when it failed was determined to be approximately 100% which is below the maximum red line speed of 111%. Had the No. 3 engine not failed on the National Airlines flight, there would have eventually been a similar failure on that model engine at some future time in revenue service.

It is also important to recognize and be on guard during the investigative phase of accidents/incidents for red herrings or preliminary findings/observations that may not be relevant and may detract from determining the true root cause and necessary corrective actions for the event.

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