Oriental Land Company has released a report on the cause of the December 5, 2003 incident on the "Space Mountain" attraction:
January 21, 2004
Oriental Land Co., Ltd. Cause of the Space Mountain Incident Determined at Tokyo Disneyland Park
Oriental Land Co., Ltd. announces the completion of the investigation into the incident which occurred on December 5, 2003 at the Tokyo Disneyland
attraction Space Mountain
. The attraction is scheduled to reopen in mid-February upon implementation of the required improvements. 1. Cause of the incident a. Direct cause of the axle breakage
The incident occurred when the axle of the ride vehicle's rear wheels broke, causing the vehicle to derail during the operation of the attraction. Detailed analysis and investigation were conducted focusing on the cause of the breakage. It was determined that the gap between the axle which broke and its bearing exceeded the design specification. This wider-than-specified gap resulted in excess play between the axle and its bearing and caused more vibration than normal during the operation of the vehicle, placing excessive stress on the installation screw nut at the tip of the axle. This fatigue fracture of the axle was the direct cause of the breakage.
While the design specifies that the gap between axle and its bearing should be about 0.2 mm, the actual gap in this case was over 1 mm. b. Reason for the gap being wider than designed
The axle that broke was one of 30 axles received in October 2002. All 30 axles were thinner than the design specification, which resulted in the gap between the axles and their bearings to be greater than the specified width. This abnormal situation occurred due the following:
In September 1995, the design specifications for the size of the axle bearing for Space Mountain vehicles was changed from inches to the metric scale. Accordingly, the axle diameter was also changed, in this case from 44.14mm to 45.00mm. However, appropriate action to revise and maintain the design drawings was neglected. Consequently, two different drawings existed within our company after the changes were made and the old drawing showing the 44.14 mm diameter was used to order (in August 2002) the axles that were delivered in October 2002.
It has been confirmed that other axles ordered and delivered between September 1995 and October 2002 were all of the required size (45.00mm).