On May 5th, 2007, a six-car stand-up roller coaster Fujin-Raijin II, during a ride, dropped one of its two wheel assemblies from the second car. Losing its balance, the second car tilted to the left by about 45 degrees. The rider in the left side of the front row jammed her head between the passenger support structure and the handrail of the maintenance walkway and was killed instantly. The next day, the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) instructed a nationwide inspection of similar attractions.
Investigations revealed that the main axle had a crack caused by metal fatigue and the owner of the amusement park, bankrupt in 2009, had been running the coaster for 15 years without changing the axle and reporting “in good condition” upon visual inspection only. The applicable law required, and still does, annual testing with magnetic particles, ultrasound, or liquid penetrant. The axle, at the time of its failure, had only about 25% of cross-sectional area remaining intact where the crack had grown. A maintenance worker later reported looseness with the axle fit in the pressure-receiving hole. The fit was originally designed tight to receive the bending force.
People pay and wait in long lines for the excitement of unusual thrill from short amusement rides. The rides take passengers through unusual movements and G-forces to make them scream and laugh. Mechanical parts of the vehicles thus are subjected to unusual loading conditions. Machine design for such rides requires serious design reviews, failure analysis, frequent inspection, and thorough maintenance. Engineering ethics call for amusement park owners’ and workers’ awareness of design and operations for an unusual environment.