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Accident on Big ThunderDOSH releases Big Thunder Mountain Railroad accident report[This article originally published in the Disneyland Park Update for December 1, 2003.]The State of California Division of Occupational Health and Safety released its report on the September 5 fatal accident on Disneyland's Big Thunder Mountain Railroad attraction. The timing of the report—released the morning before Thanksgiving, just as the news media turned their attention to the traffic in airport parking lots around the country—could not have been better for Disney officials had they scheduled it themselves. By the time the major news outlets picked up the story, the official report had even disappeared from the DOSH Web site. Even so, the contents of the report were sufficient to guarantee national headlines on both Thursday and Friday. The investigators determined that Disney's maintenance and procedures were responsible for the accident, which killed 22-year-old Marcelo Torres, and injured 10 others. The report cited two key mechanical failures that contributed to the accident: an incorrectly installed guide wheel, and a missing safety wire. The investigator interviewed workers who didn't know the difference between a "yellow-tagged" ride vehicle, (not yet ready for passengers), and a "green-tagged" ride vehicle. Machinists admitted signing for work that they had not personally performed, and managers admitted signing off on repair work that they did not personally inspect. Ride operators complained that there was no policy explaining what to do when a ride vehicle was making an "unusual sound"; noises like the train involved in the accident was making before it was sent out on its final, fatal trip. The report concluded that the design of the coaster was not to blame for the accident, saying that "there is no evidence that the design of the Big Thunder Mountain attraction is unsafe." Once the damaged track is replaced, Disney must demonstrate compliance with the "Corrective Action Specifications" detailed in the report before reopening the ride. These include retraining machinists and managers in proper procedures, and implementing a resort-wide policy for dealing with "unusual noises" from ride vehicles. Disneyland issued a statement after the DOSH report was released, saying "We agree, as DOSH concluded, that the design of the attraction is safe." The resort laid the blame for the accident on "...a failure to follow procedures...," and said that it had already "begun re-training our maintenance personnel on our policies, procedures and guidelines." The statement concluded by saying "At no time have we ever done anything which we believe would compromise the level of safety required for the safe operation of our attractions" MousePlanet has a full PDF copy of the DOSH report online (link). The 22-page document provides a detailed description of the events leading up to the accident, and the investigation that took place afterwards. Timeline of the accidentAnalysis by MousePlanet staff Tony Phoenix and Kevin Krock.On September 5, 2003 at 10:30 a.m., 90 minutes after park opening, BTMRR train #2 was put into service, making it the third operating train of the day. The report indicates that the train had been used for a show check prior to park opening. At some point during its operation, one of two bolts holding the left side floating axle upstop/guide wheel fell out. Fifty minutes after being put into service, at the conclusion of its twelfth trip of the day, the second retaining bolt fell out, causing the wheel to fall off just before it entered the station.
This retaining wheel is located under the track tube below the wheel indicated by arrow #1 in the photo above. The Big Thunder Train engine and cars are secured to the track by what can be the visible wheel on the topside of the track, and the upstop wheel underneath, which you can see figures #1 and #2. These two wheels pinch the track, keeping the car pointed in the correct direction and preventing it from lifting up off the track. The floating axle means that the axle can pivot, allowing the car to swing around curves and bends in the track. Think of a rear-wheel drive car, with a rear axle and wheels that turn.
At this point, the train entered the station and the passengers disembarked. Several cast members say that they heard an unusual noise coming from the train, and decided to remove the train for inspection by maintenance after it completed one last run. At 11:17 a.m., the train was set onto the track with approximately 24 people on board for its thirteenth run of the day. The train ran normally through the first third of the ride, climbing through the bat cave, up the lift in the rainbow cavern, and through the first drop. It ran under the tree with the swinging possums, through a steep banked right-hand turn, and into the entrance of the long, dark tunnel located before the second lift hill. The second lift hill has a steam engine off to the right hand side, and is commonly known as the location of the goat trick. The forces encountered by the train in the banked curve caused the axle to shift left, and the remaining upstop wheel on the right side to drop lower. That wheel struck a railroad tie just at the entry to the tunnel. The axle continued to drag and bounce as the train approached the small incline at the mid-point of the tunnel. This incline is also the location of the Zone 1 safety brake—brakes on rides such as Big Thunder operate with two bars covered with a lining that squeeze together. A guide on the train cars are pulled through these two bars, while the lining creates friction, slowing the vehicle. Figure 3. A rear view of the engine showing the shifted axle.
When the train engine reached the safety brake, the wheel struck the brake, damaging the brake lining and brake sensor. Because of the damage to the brake sensor, the ride computer immediately prevented new trains from leaving the station. For cast members, this "dispatch inhibit" condition was the first indication that something had gone wrong. The axle assembly then wedged between a brake and a railroad tie, causing the rear of the engine to lift off the track and to strike the first passenger car. The lifting of the engine also caused damage to another brake sensor, triggering another warning in the control center. Figure 4. A side view of the ride showing the initial collison of car #1 into the back of the engine.
The front—or nose—of the engine car collided with the last brake, shearing the brake completely off. This also caused the towbar (identified as arrow #2 in the photo) to fail. The first passenger car pushed under the engine, wedging the engine between the tunnel roof and the passenger car. The front seat of the first passenger car sustained serious damage, and it was this impact that likely killed Marcello Torres, who was seated on the front right seat of car #1. The impact also caused the rear axle of the second passenger car to derail, and the second car pitched up in the back. Figure 5. A side view of the ride showing the second collision.
The train continued to drag in this position for a bit longer until the second passenger car struck a brake, bringing everything to a stop. The forward motion stopped, and the train, now without its engine, began sliding back down the incline until a brake caught part of one of its rear cars. The ride computer sensed a train at the brake for a second time, and issued an immediate Emergency Stop command, stopping all motion on the track. Cause of FailureThe entire accident can be traced back to the upstop wheel that fell off. The DOSH investigator found the two bolts and washers that should have held the wheel in place along the track. Closer inspection (and metallurgy testing) confirmed that the bolts had never been secured tightly. In addition, missing was a safety wire that should have prevented to bolts from coming out. As a result, the wheel fell off, triggering the chain events that led to the crash. The investigation focused on Yellow and Green maintenance tags. These tags indicate which vehicles are cleared to be used with passengers (Green Tags), and which are still undergoing maintenance (Yellow Tags). Interviews of the machinists assigned to Big Thunder revealed "an inadequate understanding" of how the tag system worked. The machinists also commented that they were shorthanded.
Managers showed an understanding of the procedures, but admitted that they occasionally signed off on the work without actually reviewing the work or reports. The investigator found that the maintenance procedures were adequate, so long as they were followed correctly. In this case, they apparently were not. What DOSH has told Disney to doDisney has been told to retrain all outside machinists and managers on company policies and procedures, and to establish procedures for ride operators on what to do when they hear unusual noises. In the future, any car added to the ride must complete one full run before passengers can ride. Finally, only the machinists performing the maintenance work can sign off that the work was complete. Thoughts, questions, or comments? Contact us here. |
MousePlanet provides detailed coverage about the accident history of Disneyland's Big Thunder Mountain Railroad roller coaster. The main page with the most recent updates is available here.
The Big Thunder Mountain Railroad experienced an accident at approximately 5:30 p.m. on Thursday, July 8, 2004. Read our original breaking-news coverage of this accident here.
The Big Thunder Mountain Railroad experienced an emergency stop on Saturday, April 3, 2004, less than a week after it reopened from the 2003 accident. No injuries were reported for this accident. Read our coverage of this accident here.
A locomotive on the Big Thunder Mountail Railroad in Disneyland's Frontierland broke loose at approximately 11:20 a.m. on Friday, September 5, killing 1 man and injuring 10 others. • Our main page about the
accident (9/13/01). • The Big Thunder Mountain Railroad locomotive broke loose from the rest of the train at 11:20 a.m. on Friday, September 5, 2003. • Single fatality: Marcelo Torres (22) from Gardena, California, of undisclosed causes. • 10 injured victims, including the following, who were transported to the University of California Irvine Medical Center:
• Designed and manufactured by: WED/Walt Disney Imagineering • Ride type: “Mine train” type roller coaster • Opened: September 2, 1979 • Maximum height: 104 feet at the top of Big Thunder Peak • Maximum capacity: 32 • Height requirement: 40 inches tall (3 feet 4 inches) [correction] • Safety restraint: Single bench-wide lap bar (bench sits two) • Speed: 28 miles per hour • Disneyland's BTMRR was created in-house by Disney Imagineers. The WDW version was built in 1980. The Disneyland Paris version was built in 1992.
Discuss this incident on our MousePad discussion board. Submit info: We update this page as news becomes available. If you have some news to share, contact Lani Teshima. Comments? If you have some comments about the accident or about our coverage, please write to our MousePlanet Mailbag.
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