The National Transportation Safety Board, Washington, recently issued its report about the cause of the landing-gear collapse of a FedEx cargo plane as it landed in Fort Lauderdale in October 2016.
Metallurgical examination of a 3-by-3-inch fragment of the left MLG and the mating fracture region on the largest piece of the fractured left MLG found indications consistent with an overstress fracture having emanated from the air filler valve bore. The overstress features emanated from a small thumbnail crack, located at the radius between the cylinder inner diameter surface and the air filler valve bore surface. This thumbnail crack was observed on both mating fracture surfaces of the MLG and the 3-by3-inch fragment, and it exhibited features (such as crack arrest marks) consistent with a preexisting crack that progressed to fracture of the MLG.
The observed features in the initiation region of the thumbnail crack were found to be consistent with fatigue cracking, as exhibited by the fatigue striations observed during microscopic examination. Later propagation regions of the thumbnail crack revealed features consistent with mixed mode fatigue, overstress, and Page 2 of 23 DCA17MA022 intergranular fracture. These findings confirmed that once the crack progressed to a critical length, the left MLG cylinder fractured in overstress due to the loads imposed during landing.
Read the entire 23-page report here:
