Fatigue fracture of a main landing gear swinging lever in a civil aircraft

The left-hand main landing gear (LH-MLG) of a civil aircraft collapsed during the take off due to the fracture of its swinging lever, which is manufactured from a forged block of an aluminium alloy and certified using the fatigue safe-life criterion. From the visual examination of the fracture surface, it was possible to observe typical beach marks indicating the occurrence of fatigue failure. Further examinations by using field emission scanning electron microscopy (FESEM) as well as X-ray energy dispersive spectroscopy (X-EDS) and metallography have shown the fatigue was promoted from pre-existing material defect located on the external surface due to an abnormal silicon concentration at the initiation crack site and was likely associated with the manufacturing process. The stress analysis of the component carried out by means of finite element analysis (FEA) also confirmed the origin of the fracture was located at the most stressed area and the simulation of the crack propagation by means of AFGROW analysis pointed out the propagation started in the early stage of service. As a consequence of that, all the swinging levers coming from the same cast batch were removed from service.