During the manufacturing of the low-pressure shaft, at a location where its section diameter increases, a sharp, 90-degree step was made, resulting in a sudden diameter change over a very short linear length - a classic condition for stress concentration, which results in fatigue cracking at that location. Additionally, the metallurgical analysis found that the shaft was incorrectly heat-treated during manufacture and contained contaminant particles such as non-metallic inclusions, which further reduced the shaft's ability to carry the torsional loads as designed. The improper machining and impurities facilitated an accelerated fatigue fracture of this key engine component via unmitigated formation of micro-cracks through the shaft's core, ultimately leading to its failure.