McDonnell Douglas DC-8-63F, 9G-MKO
The aircraft’s right main landing gear suffered extensive fracturing of its shock-strut piston as the aircraft was making a 180° taxiing turn. Associated disruption to the landing gear scissor linkage allowed the landing gear truck to diverge approximately 45° from the aircraft’s heading, but one of the broken parts of the piston remained jammed in the shock-strut cylinder and continued to support the aircraft. Around 90% of the specified overhaul life of the landing gear remained at the time of the accident. Specialist examination indicated that the piston material was in accordance with the aircraft manufacturer’s specification. The fractures had originated from a small pre-existing stress corrosion crack in an area of the surface where cadmium plating was absent. The crack had probably been initiated by abnormally high local stresses associated with a step in a blend radius in the region of the crack origin and with surface scratches in the area. These features should have been apparent during the last overhaul of the landing gear. The pre-existing crack, while small, was probably sufficient to cause the rapid extensive fracturing of the piston under normal operating loads, given the notch sensitivity of the high-strength steel from which it was made. One safety recommendation, relating to the Federal Aviation Administration’s oversight of overhaul organisations has been made.
9G-MKO-3-05.pdf (514.46 kb)