The Fractographic Investigation of an Aeroengine Accessory Gearbox Quill Shaft

This paper analyzes the fracture of the quill shaft. An investigation of a twin-engine trainer aircraft incident has been reported. The incident occurred due to the right electric generator out and low oil pressure. The main failure based on the warnings and the subsequent incident was identified. The failure involved the fatigue fracture of the quill shaft on the J85 turbojet engine's accessory drive gearbox (ADG) and Input Drive Assembly (IDA). It was determined that the fracture had been originated by the torsional loads impacting the quill shaft that connects the ADG and IDA. The quill shaft was broken as the loads excessed the limit values designed by the manufacturer as a system protection part. Although the main failure was successfully identified, further analysis regarding the reaching to the triggering cause of the fracture was performed. Through the detailed fractographic and metallographic studies, the root-cause of the fracture was determined as the misalignment of the quill shaft between ADG as the driving unit and IDA as the driver unit.