The middle portion of the lift line.Near the top set up for bike operations.View down from the summit.Single-leg drive station.Leitner detachable controls.Murray-Latta bike carriers.Drive station from below.Loading area.Depression tower 1.Leitner “pancake” return station.Return arrival side.Lift line view from the base lodge.Leitner Report entry.
I heard that there was a storm of unlikely problems that happened at a time causing the crash. Form the news picture it did not look like the bar was down. If the bar was down they may have stayed on the chair, or there would have been less chance of falling.
With the way the chair was swinging according to witnesses that bar would not have kept them in. Especially given the fact that the bar is not latched down and moves up and down freely.
As a response to Johnathan. I don’t think the bar being down would of helped. 50% of accidents happen with the bar down and 50% with the bar up. I can’t blame them for having the bar down. Really it was a bad day for the lift to be running, so the winds were really the cause. It had high winds and the chairs were shaking violently. Also I heard that the lift was having problems anyway with the drive. It was bought from a third-class company. It was replaced the next season after the accident.
1. How does a drive defect/malfunction cause the lift to swing from left to right if the the lift only pulls forward to back? I don’t know if its an obvious thing i’m missing or what.
2. What modifications were made to the drive?
3. What brand drive did they replace it with and what other replacements were made?
I don’t know the answers to 2 or 3, but I can speak to #1. If you’ve ever ridden a lightweight double chair of any sort, you’ve probably experienced a similar (although less violent) process. If the carriers swing forth and back enough (as in a misload or a poorly maintained ramp) that motion eventually translates into a side-to-side direction. I don’t know the exact physics behind it (precession, maybe?) but I’ve seen and felt it many times.
It is a form gyroscopic procession but not a clean one. essentially the entire hanging mass wants to spin. It can’t spin past the grip/rope, and as a result that momentum is transferred as close as it can get to doing full 360s; a side to side swing.
You’ll also notice you can control this slightly while riding by spreading yourself and any other riders out, while if you squish together in the middle it will speed up.
To piggy-back on rbropetech’s comment, the surging would’ve caused the carriers to “bounce” vertically, which then generally causes them to swing relatively unpredictably. A key point though is this wasn’t really a drive malfunction, so much as a drive tuning problem. As the line was surging (from repeated changes from fast->slow->fast in quick succession under certain loading conditions) the drive would continue to “hunt” for the proper speed that would perpetuate the oscillation that developed in the line.
The entire report from the CTSB is floating around on the CTSB website, and if you’re interested in the gritty details about how motor controls on ski lifts work, it’s worth a read. But the gist of it was the original analog Control Techniques DC drive was replaced with a new digital ABB drive. The drive itself was replaced and some sort of interface with the original low volt controls was installed, but the rest of the low voltage controls remained intact.
If you’re concerned about the new drive, it was (at the time of install) the flagship ABB DC drive and absolutely an industry standard. That product just has an incredible amount of power and flexibility in how it can be configured for all of the different applications it might be used in.
Lift Blog 
http://www.thedenverchannel.com/news/investigations/state-board-votes-ski-resort-did-not-violate-law-before-mothers-fatal-fall-from-chair-lift
LikeLike
Here comes the lawsuit
LikeLike
I heard that there was a storm of unlikely problems that happened at a time causing the crash. Form the news picture it did not look like the bar was down. If the bar was down they may have stayed on the chair, or there would have been less chance of falling.
LikeLike
With the way the chair was swinging according to witnesses that bar would not have kept them in. Especially given the fact that the bar is not latched down and moves up and down freely.
LikeLike
What is the model of this lift?
LikeLike
SA-4 Compact, most likely. Michael would know.
LikeLike
Yes, take a at the report in the last picture: it says SA 4 C, where C stands for Compact.
LikeLike
As a response to Johnathan. I don’t think the bar being down would of helped. 50% of accidents happen with the bar down and 50% with the bar up. I can’t blame them for having the bar down. Really it was a bad day for the lift to be running, so the winds were really the cause. It had high winds and the chairs were shaking violently. Also I heard that the lift was having problems anyway with the drive. It was bought from a third-class company. It was replaced the next season after the accident.
LikeLike
1. How does a drive defect/malfunction cause the lift to swing from left to right if the the lift only pulls forward to back? I don’t know if its an obvious thing i’m missing or what.
2. What modifications were made to the drive?
3. What brand drive did they replace it with and what other replacements were made?
LikeLike
I don’t know the answers to 2 or 3, but I can speak to #1. If you’ve ever ridden a lightweight double chair of any sort, you’ve probably experienced a similar (although less violent) process. If the carriers swing forth and back enough (as in a misload or a poorly maintained ramp) that motion eventually translates into a side-to-side direction. I don’t know the exact physics behind it (precession, maybe?) but I’ve seen and felt it many times.
LikeLiked by 1 person
It is a form gyroscopic procession but not a clean one. essentially the entire hanging mass wants to spin. It can’t spin past the grip/rope, and as a result that momentum is transferred as close as it can get to doing full 360s; a side to side swing.
You’ll also notice you can control this slightly while riding by spreading yourself and any other riders out, while if you squish together in the middle it will speed up.
LikeLiked by 1 person
To piggy-back on rbropetech’s comment, the surging would’ve caused the carriers to “bounce” vertically, which then generally causes them to swing relatively unpredictably. A key point though is this wasn’t really a drive malfunction, so much as a drive tuning problem. As the line was surging (from repeated changes from fast->slow->fast in quick succession under certain loading conditions) the drive would continue to “hunt” for the proper speed that would perpetuate the oscillation that developed in the line.
The entire report from the CTSB is floating around on the CTSB website, and if you’re interested in the gritty details about how motor controls on ski lifts work, it’s worth a read. But the gist of it was the original analog Control Techniques DC drive was replaced with a new digital ABB drive. The drive itself was replaced and some sort of interface with the original low volt controls was installed, but the rest of the low voltage controls remained intact.
If you’re concerned about the new drive, it was (at the time of install) the flagship ABB DC drive and absolutely an industry standard. That product just has an incredible amount of power and flexibility in how it can be configured for all of the different applications it might be used in.
LikeLiked by 2 people