Six Flags Pendulum Ride Closes After Shaking Incident

Incredibly bad or incomplete engineering - resonant frequency determination and failure mode analysis are not exactly new to the mechanical engineering world.

I don't think I will ever get on one of these rides after seeing this.

I've been working in the amusement park industry for 25 years and my brother has been working in the car industry for the 25 years. We both have always said the same thing: don't buy Italian. Great with food terrible with engineering lol.

I think if they change the motor's idling speed, it will probably solve the problem. This reminds me of the famous Takoma Narrows Bridge disaster from 1940, which is a case study for resonance in engineering.

It’s typical for Six Flags to hire cheap labor with hardly any oversight. Glad no one was hurt.

@AgustinMacias - What are you talking about? This pretty clearly is a result of poor engineering by the manufacturer, and has absolutely nothing to do with the ride ops, maintenance, and/or management/oversight. Six Flags isn't the first, and certainly won't be the last, park chain to get burned by a manufacturer error.

If someone wants to do the math - how much guest imbalance would operators have to load on a ride like this, for how many cycles, to achieve a resonance problem like this? Is it even possible for operations to contribute to this?

Por que no los dos? Ops should've hit the emergency stop a lot faster than everyone could pull their phones out and start recording.

@Russell Meyer

That’s who I was referring to. I don’t blame ride ops or technical maintenance of the park on this, I blame the cheap, non-union contract engineering work that Six Flags often hires to build the rides.

this is horrifying as i really love these rides but when i rode the one at six flags over texas in 2019, there was a very noticeable thump, both in sound and feel, on each downswing that was quite unnerving. shortly after, i saw the video of the collapse of the mock version in india and will probably never ride one of these again.

@AgustinMcias - What does union/non-union have to do with anything? There are plenty of firms utilizing union labor that do subpar work, so trying to paint this as a union/non-union argument shouldn't be a root cause until all of the details have come to light.

Also, let's be clear, there are two completely different sets of contractors involved with a new ride like this. First, there is the manufacturer, in this case Zamperla. Six Flags most likely has a mulit-attraction contract with Zamperla for a set number of these attractions from the Italian manufacturer that are slightly modified to meet the specifications for each park (mostly size modifications). Second, there are many different contractors that are hired to perform the actual installation of the ride at the park. After the pieces of the attraction are delivered to the site, a host of different contractors complete the installation. FWIW, 99.99% of all steel erection companies (the contractors responsible for assembling the frame and structure) utilize union labor. I can't say for certain that was the case here, but almost every erection company in the DC area is union. After the structure is assembled, there are various other trades (some likely using union labor like electricians) that come in to complete the installation. Once all of the assembly is complete, the manufacturer typically has representatives inspect and test the attraction to ensure it's working correctly and hands off operation to the park (these reps will usually walk the attraction through state/local inspections too). Once the attraction is in the park's hands, the park is responsible for maintaining the ride according to the O&M (operations and maintenance) manual provided by the manufacturer. This manual is usually a pretty regimented document that provides part replacement schedule, operational specs, and troubleshooting guides (similar to a car owner's manual but far more complicated). Manufacturers also provide support if unexpected issues (like this one) arise that cannot be diagnosed by park staff.

There certainly could have been an issue during the installation of this attraction, but it looks like this an unforeseen function of a uniquely sized structure where the idle speed of the motor (mounted at the top of the structure) happened to resonate at the same natural frequency of the legs. This appears to just be a strange fluke of engineering that happens, and cannot always be predicted. If anything the manufacturer (Zamperla) would be responsible for this, and would need to work to find a solution (vibration damper or changing idle speed). Pointing the finger at contractors assembling, breaking in, or maintaining the ride is almost certainly erroneous in this case. Trying to claim Six Flags use of "cheap non-union labor" to assemble the attraction caused this incident is even more laughable. Even blaming the manufacturer is probably a step too far, because this ride model has a pretty decent track record of performance not only in the US, but elsewhere around the world. Again, this unique length of the legs coupled with the idle speed of the motor (or other vibration sources like wind speed) almost certainly caused this issue, and can easily be chalked up to an unforeseen fluke. That doesn't take Zamperla off the hook for fixing the problem, but this isn't the same situation as Intamin's multiple instances of designing attractions/maneuvers that place extreme forces on riders' bodies (Maverick, Intimidator 305, and Perilous Plunge).

@Russell -- Six flags bought a handful of these rides and installed them across the country. Obviously, there are some variation in size due to space restrictions in a given park, but do you know if there are any "similarly sized/designed" Zamperlas at either Six Flags or others parks? It would seem that if there was an identical ride in another park, it too should be shut down until a solution to the resonance issue is found.

This is a huge problem for Six Flags, and I can relate to it from personal experience.

Over the last 4-5 years, my organization has spent hundreds of thousands of dollars paying for load studies on our telemetry towers here in NW Florida. Part of the work was for determining resonant frequencies when a different antenna was placed on top of the tower, part was for stability analysis, and part was for hurricane survivability. One of our towers was identified as being at risk for failing if hurricane winds exceeded 130 knots. Six months after the study was complete, that particular tower experienced wind gusts up to 150 knots during Hurricane Michael. Everything around it was knocked down or severely damaged, but that tower came through unscathed. Other radio towers that were expected to survive did not.

So what I'm trying to say here is that you can do a lot of studies and computer simulations to identify problem areas, but sometimes things in real life don't follow the parameters that we try to impose on it. In the case of this ride, it appears that there was just enough variance in the real world conditions from the modeled conditions that an unidentified problem surfaced.

From the short video, that was included in this story, I'd say that a partial if not complete disassembly of the ride is required with extensive NDI of the critical components and connectors. A complete analysis of the cause of the problem as well as a complete analysis of the solution has to be performed. None of this is inexpensive. Then somebody at Zamperla or Six Flags has to sign off that this ride is safe. Yes, the State of Maryland has to clear the ride for operations, but Six Flags and Zamperla and their insurors have to assume the risk. If I'm the guy that has to make that decision, I'm not doing it. There's just too much downside risk for far too little gain.

The best thing to do is to quietly disassemble it and pretend that it never existed. Take your losses now and move on.

@MLB - This is one of the smaller versions of these installed as part of the most recent wave of additions at Six Flags parks. The ones in California (Crazanity at SFMM) and New Jersey (Wonder Woman Lasso of Truth at SFGAdv) are both @20 feet taller (SFAdv's tops SFMM by @2 feet) and are categorized as "Giga Discovery" by Zamperla, but pretty much every Six Flags park in the US has installed a Giant Discovery over the past 3-5 years. I don't think there are any 2 that are of the exact same height/configuration (most are in the 140-160 foot range except for the "Giant Discovery' models, which are both @170').

I don't necessarily think a full disassembly is necessary. Inspections and tests can be done to the structure while it's standing to ascertain whether there are any structural/manufacturing defects that caused the incident (it could be something as benign as damaged/missing motor mounts that dampen the vibration). There are a lot of other variables that could have led to this (weather, load balance, ride cycle, etc...), which may necessitate a full review of the design by the manufacturer (that could force all models off line for a while), something I think both Six Flags and Zamperla would prefer to avoid given the popularity, and otherwise solid track record with these rides. While this definitely appears to be a 1-off caused be specific variables in play with SFA's installation, if another model experienced a similar issue, both Zamperla and Six Flags would be in deep trouble.

I totally understand, Russell, but if something does happen with any of these rides for any reason and somebody gets hurt or killed, a trial lawyer would have a field day with this video regardless of the cause of the problem. The risk of a huge financial and PR disaster is just not worth any gain of trying to keep this relatively inexpensive ride.

I can say from my experience that NDI'ing ride components and finding defects does happen, modifications are made, and the rides continue operating. I haven't been paying close attention to this in years but in the early 2000's there was a well known manufacturer that had a major problem with this (I won't say the name but it starts with the letter I and ends with ntamin).