This paper presents the fatal damage of a twin-spool turbofan engine due to fan blade off during an active stabilization test. When performing some active stability control measurements, a slight surge occurred which was followed by a blade off incident in the first rotor of the low pressure compressor. This accident led to a fatal damage of the entire engine. All following components and modules have been affected and partially badly damaged. Since the failure was contained, beside the inner components of the engine no other parts, no outside equipment and no accessories have been damaged. After the accident the engine was detached from the test bed and completely dismantled. A detailed mechanical, metallographical and analytical investigation has been performed. The result of it brought the evidence that a fatigue fracture was the reason for the breakdown. Additionally, the analysis confirmed that the active stability control measures did not excite any vibrations and therefore did not contribute to or cause the fan blade off. For the investigations low and high frequency measurement techniques are applied to gather all informations with respect to benefits in surge margin, additional operating range and reasons for instabilities and their pre-cursors. The results of the analyses are displayed in photographs of the damaged parts, recordings of the microscopic examinations and in diagrams and compressor maps. The outcomes demonstrate that after the throttling of the LPC until its stabilization boundary a short and slight surge occurred, followed by a drop of the relative corrected spool speed line. After that a second decline of the mass flow appeared and the engine was running down. The inspection under the microscope showed oscillation stripes on the surface of the cracked blade, being an evidence for a fatigue fracture.
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