The Case of the Crumpled Airplane Seat
Head-rest components from a passenger’s seat in a jet plane crash were dissembled and examined. The failed parts were believed to have contributed to a passenger’s injuries. The damaged components were the subject seat frame, backrest, headrest and track extrusions. Fracture surfaces were cleaned by non-invasive techniques to remove debris. The subject seat frame, backrest tubes, brace tubes, rivets and screws were damaged and photographed. The structural tubes of the subject seat frame and backrest were mis-aligned and awkwardly bent. An exemplar seat was used for comparisons of the head-rest tube integrity and compliance with the Original Equipment Manufacturer (OEM) specifications.
The subject headrest revealed evidence of unintended, longitudinal sweep, twist, and distortion in the support tubes. Fractures, micro-fissures and failed threads were examined to 40X. Determinations of surface irregularities and failed thread separations were recorded. Measurements, ultrasonic tests and x-ray examinations of the subject tubes were compared with the exemplar tubes and manufacturer’s data.
Headrest tubes were damaged in the subject passenger seat as a result of the crash. The fracture surfaces of the tubes failed in the ductile fracture mode. The directions of failures were toward the back of the aircraft. Fracture initiation sites were on the outer holes drilled in the tubes and threads. Several tube threads were stripped with ductile deformation. The bent tubes were thinner in the outer radius.
The Lessons Learned:
The shear fracture damage resulted from an impact overload. There was no evidence of base material discontinuities or abnormalities. The ½“OD tubes were aluminum 6061-T6 with a load capacity of 3200 pounds. It was determined that the subject tubes, bends and failed threads were manufactured in accordance with the OEM specifications.