Cedar Point guest hit by Top Thrill Dragster part while in queue

In the video (during the Q and A) they state that the park is in possession of the object and that is has been thoroughly inspected; that said, it does indeed match the object from the post where the person was supposedly keeping it. It seems that was legit. They also state that they have not yet calculated how far the object flew...it is not yet determined exactly when it became detached from the train.

I guess my faith in humanity is somewhat restored in that he apparently had a change of heart and chose to turn it in.

I'm trying to picture how this bracket is attached. Does one side of the bracket hang down vertically like a fin (with the bolted side on the underbelly) for the sensors to pick up on?

This is about as bad as it gets with regards to what we were collectively thinking.

Jeff said:

Summary: The "flag plate" apparently used to interact with proximity sensors on the track came loose, and the inspection showed impact from the plate on several track ties around the "finish line." Some of the bolts that held it in place were still on the train.

That's interesting, because I assumed that the sensors all keyed off some part of the train that was already there, like the wheel bogies or the spine of the car. I'm surprised that there was a plate specifically hanging down for that purpose. I'm also surprised to hear him say it's on the left side, because at least outside of the station, the prox switches are all on the right side of the kicker wheels.

I'm surprised by that, too. I can see this being the case on something like Blue Streak where it used to operate with common sense instead of sensors, but in general if a ride is designed to use proximity sensors, they sense a component of the train. If for no other reason than cost savings... why add a metal piece when the entire structure of the train is metal?

These days the common way to do it is to count the brake fins. But guess what: Dragster doesn't have brake fins on the train.

This method used to be common. Back when rides used whisker switches, there would be a flag hanging down on the front of the lead car and at the back of the last car, one on each side. Later we saw little ones used for prox switches. Typically there will be switches on one side for check-in and on the other side for check-out, and accordingly the block system apparently has, in this case, a check-in switch on the right, and a check-out switch on the left. Look for pairs of prox switches, these are the ones tripped by these flags.

I wonder if Dragster uses this method instead of counting axles or anything like that because of the high speeds involved. Already we know that the flag is bigger than what I've seen on other rides, and that makes sense because at 120 MPH, an 8" flag is going to be in the range of the prox switch for slightly more than 3 milliseconds, which is barely enough time to trigger a 600 Hz switch, assuming I did my math right. I wonder if it makes more sense to use latching inputs and discrete check-in and check-out switches because trying to count the axles as they go by (for instance) may be pushing the limits of what the PLC can reliably detect. Since you don't care about the middle of the train (only the front and back ends) a pair of latching inputs mean you don't have to worry about missing the train as it enters or leaves the block, even if the trigger happens faster than your detection loop code can run.

I also wonder if the flags are modified from the original design; if Cedar Point switched to longer flags than Intamin originally provided, or even switched to the flags from some other detection method. I heard that back when the ride was new, they were having problems reliably triggering the sensors at some of the faster points on the ride, and the solution to that problem would be to both switch to faster sensors, and also to use longer targets (flags) on the train. That said, this is a modification that would have been made back in 2003 and by this time would be considered "service proven" by just about any reasonable observer.

--Dave Althoff, Jr.

How could both bolts fail at the same time? Could it be that the bolts on the plate were over/under torqued?

Yes, if the lot is fasteners is bad it is possible. I have first hand experience with that using flight, Qual-1 hardware on space hardware.

I just posted this on Pointbuzz, ill cross-post it:

Even if proper grade hardware is used, performance isn't guaranteed per-say. Flaws are possible (voids and other defects) that can jeopardize the hardware.

We have had flight hardware fasteners (highest quality level required with material certs, testing, traceable source, etc...) be defective before upon installation... For example, a few weeks back we were applying the appropriate torque and the head of a fastener sheared completely off. We were not pushing these fasteners to their limit by any means. After investigation, we found the undercut/relief groove between the top of the thread and the fastener head was at too small of a diameter, reducing the strength significantly. I don't remember off the top of my head, but I calculated something like a 40-60% reduction in strength (note, these were relatively small fasteners, so it wasn't as easy to spot visually). Even if the fastener torqued up properly, it most certainly would have failed under vibe/shock testing. Which would have been far worse for us, at least. We ended up ordering in all new hardware and discarding that lot and pre-inspecting each for the appropriate diameter of the relief.

Things happen... Unless you do NDT on each and every fastener and doing a full dimensional check on each and every fastener, your hoping redundancy (having two fasteners when only one is required, for example) and FOS in design can prevent critical failure like this. If this was a bad batch of hardware, there is little that could have been done to know ahead of time without testing each and every fastener, which isn't common by any means.

Not knowing really anything else on this one, my bet is on defective fasteners or installation (overloading the fastener with the wrong torque value or a combination of the wrong grade fastener / torque).

This picture appears to show those brackets, on the upper inside of each bogey.

https://www.flickr.com/photos/invertalon/16048494363/in/album-72157650618870697/

I think they said at least some of the bolts where still present on the bogey, which suggests it wasn't sheared off, maybe. Perhaps the nuts loosened thru vibration?

That's it, plain as day. Weird that they're on both sides. Still, it would seem you could sense the bogie itself with a sensor that's three inches higher, assuming that there's nothing else that requires that clearance elsewhere on the train. Here's the weird part though: They only seem to be used in the uptrack standby area and in the stations and prelaunch. I haven't found any above track in the launch section, and the one on the top of the ride appears to sense the train spine, because it's centered.

macevhicz said:

I think they said at least some of the bolts where still present on the bogey, which suggests it wasn't sheared off, maybe. Perhaps the nuts loosened thru vibration?

I took “half of the bolts” to mean half of each bolt was still present, as in sheared off. The threaded portion of the bolts were still in the train… Opposed to half of the original number of bolts were still there.

I've been trying to watch a bunch of POVs in slow-motion today. It seems like there's three places along the width of the track where sensors are located. Close to the center-line, where the tire drives are, and then on the outside left and right sides where the brake fins are located. Those plates looks like they would only signal the outside rows, and I was only able to see those sensors once the train has exited the main braking block and goes into the transfer blocks back to the station. At that point, there's quite a lot of those sensors.

While I'll always trust Rideman, it doesn't appear that these plates were used for detecting block entry/exit, but rather used for precise positioning within those transfer zones.

You can see the sensors fairly well in this POV

Edit: Looks like Jeff already spotted their locations on the track too.

The more that comes out about this, the more I honestly have to say this was a very weird and freak accident. If you think about it, those fins are basically hanging inside of the rails, so if one was to simply have the bolts fall off, even on the break run, the majority of the momentum would be forward inside of the plane of the rails. It had to hit something to change it's direction and cause it to fly out to the left and the waiting area of the line.

Now, as a side note, think about how many coasters have spots where the queue is similarly close to the track... Some near brake runs... Off the cuff at various parks:
Millennium Force
Iron Dragon
Sky Rocket
Steel Curtain
Voyage
Sidewinder (and really all the boomerangs)
Storm Runner
Fahrenheit
Skyrush

Also, not saying everything is perfect with this article, but it does seem to have a few more details...

https://www.usatoday.com/story/news/nation/2021/08/24/cedar-point-a...570033001/

Walt S said:

It had to hit something to change it's direction and cause it to fly out to the left and the waiting area of the line.

They mentioned damage to the track on one of the news reports, so maybe it hit one of the angled cross-ties in the track. They are angled in a way that a object hitting it just right could cause it to go towards Iron Dragon or the line.

I imagine it could have been even more catastrophic if the part somehow got caught in the wheel or brake assemblies and caused a violent stop at 120 mph.

I would expect, now that we know what we know, that Kingda Ka would come under some scrutiny, but I haven't heard anything about it, other than passing mentions in stories about Dragster. As far as anyone here knows, is it still running?

I think the speculation about changes to the queue in order to open the ride are interesting.
This is not unlike freak accidents that happen to bystanders at sportsball games. I was at a Reds game one evening when a foul ball rendered a child unconscious. Here in Columbus there was a fatality from an errant hockey puck at an early Blue Jackets game. As a consequence we now see nets around ball diamonds and plexiglass separating the ice from the arena.
In all these cases everything was 100% safe, worry and incident-free. Until it wasn’t. Calling for the ride’s removal seems premature.

I don't think the ride will get removed. Unfortunately parts fall off rides more often then parks admit. If this part fell harmlessly to the ground instead of the freak ricochet into the queue, I bet Dragster would have already re-opened and nobody would have ever known why it closed for a few days.

At this point the park probably has a good idea of what happened and how to keep it from happening again, but it's a good PR move to keep it closed the rest of the season. (Regardless of the state not allowing it to open right now as a result.) Perhaps it will also slightly help staffing issues as well, as guests will understand why it's closed.

It's really unfortunate and I am hoping for the best outcome possible for that lady who was in the wrong place at the wrong time.

"Unfortunately parts fall off rides more often then parks admit."

Yeah... Working Steel Venom at GL during our opening test runs we had a belt buckle fly through the station at 70mph and smack the shed under the back spike. Found out an imperial fastener was used instead of metric and it backed itself out. Oops!

(note, SV had two belt buckles mounted for each seat off to the side... It was obviously one that the belt from the harness was not attached to).

I'll second that as well. Just the one summer I worked Wicked Twister years ago, I can remember a few items off the top of my head.

On one of the reverse passes through the station I remember hearing a metal on metal clang followed by a thud in the sand behind the station. I looked down and could see a shiny metal plate of some kind that wasn't there just a moment ago. Don't recall what it ended up being but it was also about the size of a palm, though it was flat and not angled. Shut the ride down and had maintenance do their thing and I believe we reopened within an hour or two.

Another time I was working at the ride entrance when a guest approached me from behind inside the line and said that something had fallen from the ride. I followed the guest to outside the rear spike and found everyone in line pointing at something under the tower. I had no idea what it was but I could see it was some sort of metal object that clearly didn't belong there. Again, shut the ride down and I also believe we reopened within a few hours. I believe that piece came from the train. It was more of a block than a plate.

Side note. Ever notice the dents on the metal panels on the awning type structure directly under both towers? Those were typically caused by items that were accidently left in the trains by maintenance and ride ops during test runs. Think wrenches, cans of cleaning spray, etc.

Those are just a few examples and as I wrote this I thought of a few more from other rides but you get the idea. Not trying to make any excuses for anyone or anything. I've personally known many park maintenance personnel over my career and all of them are very dedicated and good at what they do. And generally speaking the industry's preventative maintenance programs are very good. But unfortunately yes, "parts fall off rides more than parks admit." Even not knowing the definitive cause of the Dragster incident, I would confidently say parks and manufacturers generally do everything reasonably possible to ensure things like this don't happen. Yes, incompetency and bureaucracy have caused incidents in the industry before, but generally speaking it hasn't been a major issue. Unfortunately, it seems like things like this happen. Personally, I think there are two important questions to keep in mind. Was everything done within reason to predict, design, and prevent something from happening? Then if something does happen, how can this be prevented from happening again within reason moving forward? Personally, I think the "within reason" part is very important. It is not possible but also impractical to foresee and prepare for every single scenario.

The part I'm amazed by is that something like this Dragster incident doesn't happen more often. Just in these two examples from Wicked Twister, it was pure chance that no one was hit.

When I worked PaddleWheel, I encountered a lot of flip phones and small videocameras falling from TTD, but I don't ever recall seeing parts of the ride fall into our ride area. The park changed our exit path to keep people from being in the area that loose articles always seemed to fall into at some point, if I recall correctly. Bystanders getting hit with flying objects is an ongoing problem. It's not just loose articles. It seems like this particular incident is a wake up call for the entire industry.

macevhicz said:

This picture appears to show those brackets, on the upper inside of each bogey.

https://www.flickr.com/photos/invertalon/16048494363/in/album-72157650618870697/

I went back and cropped a better/closer pic of the part in question. This was the only image I had of the train that shows the component.

Looks like a couple of flush bolts, and the attached side of the bracket is thicker than the top. I wonder if those have nuts on the other side or if they're screwed into a machined socket hole (that seems unlikely). That photo of the guy holding the part showed a lot of wear on the underside, as if it had been dragging across some sensor that was perched too high. Again, it looks like that's only on low-speed areas of track, but I imagine enough contact would eventually loosen it.