Why Did the Fury 325 Roller Coaster Break?

After a guest recorded video of astonishing track movement on the Fury 325 “giga coaster” at the Carowinds amusement park in North Carolina, engineers scrambled to identify the cause of the failure.

In the video, when the train passes the support column, the track sways, and the top portion of the column is revealed to be completely broken off. This has left Carowinds staff, Bolliger & Mabillard Consulting Engineers Inc. (B&M is the company that designed and built the Fury 325 coaster), and the public wondering how this happened.

In response to the failure, inspectors quickly scrambled up the structure to get a look.  “In partnership with B&M, we have performed a battery of tests to identify the cause of the fracture, which appears to have formed along a weld line in the steel column,” said Carowinds in a statement released to the press. Additionally, inspectors examined the entire track, support columns, and foundation, the company stated.

The solution will be to replace the entire support column, with the replacement column arriving within a week. Once it is in place, engineers will conduct thorough tests of the repaired coaster.  “These will include an accelerometer test that uses sensors to measure any variation in the ride experience. After that, we plan to operate the ride for 500 full cycles, performing tests and inspections of the entire ride throughout that period. Once this phase is completed, we will ask B&M and the third-party testing firm to perform a final inspection to ensure the ride exceeds all required specifications,” said the Carowinds statement. 

To guard against any such failures in the future, Carowinds said that the company will begin conducting regular visual inspections employing drones to get a close look at areas that are hard to reach, like the site of the breakage in the support column.

Of course, the park already had an inspection program that should have identified this problem as it was developing. “Annual maintenance is our opportunity to dive deep into the health of ride components that cannot be seen on a frequent basis,” said Shawn Hopkins, Carowinds’ mechanical maintenance manager, in a January 2022 post on the Carowinds website. “Ride manufacturers design attractions to operate safely. Daily, weekly, monthly, and annual maintenance checks are completed to ensure the health of the ride.”

This testing requires technicians to disassemble, inspect, test, and rebuild each attraction’s cars or trains. The inspections include x-ray, ultrasonic, and accelerometer testing, and magnetic particle testing. “The process can take up to 1,600 man-hours for large rides like Fury 325,” Hopkins said. A Carowinds video posted to the company’s YouTube channel shows a purpose-built tractor that crawls slowly along the 6,602 feet of Fury 325’s track for inspections.

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With such a rigorous inspection process, we are left to wonder how this failure could have occurred. “Welds are notorious locations for raising fatigue, so it is a common issue,” observed Dallas Richards, who is a licensed professional engineer in the railway industry with structural expertise. “That is one of the most common and most unpredictable types of failures.”

While Richards works on railways rather than roller coasters, they are both defined as “engineered guideways,” though the forces involved are very different, he points out.

The welders who weld parts like the Fury 325’s support column are certified experts and their work is subsequently inspected by third parties, which should ensure the quality of the weld. However, this weld failed for some reason, and it may be there was an overlooked flaw.

“Welds are inspected but you don’t always inspect every inch of every weld,” Richards observed. “If there was a crack in the weld, if there was an air inclusion in the weld, then it can propagate.” The "Making of Fury 325" YouTube video even depicts ultrasonic weld inspection using a Krautkramer USN 58 ultrasonic flaw detector on one of the coaster's components.

The two primary ways engineers address the possibility of such failures are to apply a factor of safety to the design and to include redundancy with multiple load paths, Richards explained. Even with CAD design, “you can’t always predict the loading as well as you think you can,” he said. So engineers pad their designs with some surplus strength and load-bearing capacity.

And then they back up each support with alternate load paths in case of failure, as happened in this case. “There are lots of stabilizing members around that [broken] member,” Richards pointed out.

Indeed, Carowinds pointed this out in their statement. “It’s important to understand that rides like Fury 325 are designed with redundancies in place to ensure the safety of guests in the event of an issue such as this,” the company said. 

That safety net prevented a tragic result from this failure. Presumably, extremely careful fabrication of the new part and continuous inspections will prevent a recurrence, though the support column is highly stressed in its location at the apex of the turn.

Other roller coasters will surely find themselves under added scrutiny. And while it is harder to spot such failures before the part breaks completely, as happened in this case, it is possible. “Fatigue is tricky,” said Richards. “You can’t see it until it happens.”

When it does start, it leaves evidence. “You’ll get rust stains from the crack or chipped paint,” Richards said. “There are things you’ll see as an inspector that are indicative of cracking.”

Once B&M and Carowinds say Fury 325 is ready, then inspectors from the North Carolina Department of Labor’s Elevator and Amusement Device Bureau will take a look for themselves. Only after that bureau certifies the safety of the coaster will it reopen. “We will share an update on the reopening of the ride when a date has been finalized,” said the Carowinds statement.