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Society of Ropeway Technicians

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Society of Ropeway Technicians

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  • Montana Incident Report
  • Montana Incident Page 2
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Incident Report 3.10.25 P - Part 2

Local gust speeds day of incident, incident hour highlighted

Local Wind/Gust Plots

Unfortunately, there is no publicly available recorded wind plot. The nearest accessible plot is located in a valley just south of the resort. In back-testing with weather models there is a correlation the resort and this lower station. Interpolation of speeds would be higher at the resort. Two days before the incident, gust speed and timing run somewhat parallel to resort forecasted wind. At the time of the incident (at this station) notice, gusts no longer parallel steady-state wind and extreme direction changes at the incident time.

-Yellow bar is incident time-

18 hours of HRRR forecast blocks showing 2 - 48 hour forecasts

Forecast Model Available

Using the HRRR - High Resolution Rapid Refresh forecast model covering 2.56 x 2.56 km gridded land size. 

Wind is referenced as: Gusts @ 33’, Wind Speed @ 33’ AGL, 260’ AGL, 9900’el. The resort covers 4 grids. 

In 18 hours the resort could utilize 1,848 HRRR wind forecasts.

NWS local forecast example nearest Red lodge resort

Local Wind/Gust Plots   

Due to digital mapping limitations in mountainous terrain, the speed must be interpolated. For that reason, the simple HRRR based National Weather Service three times daily forecast must be adjusted – it will not be accurate unless this is done.

HRRR digital elevations with ropeway and parking lot shown. Typical interpolation with wind speed at

HRRR Grid with Ropeway Location

Chart shows: grids, elevations, wind forecast levels, resort elevations (green line) and Triple chairlift elevations. An interpolation shows gust speed two grids away could be more representative in this terrain. This interpolation is very common in mountainous terrain that shoots above the model’s average elevation. Notice the ropeway covers 2 grids, also these are well above grid forecast elevation.

3 levels of gust considerations

Local Gust Effects

In gust evaluation three atmospheric levels should be considered. At higher speeds, lower level terrain influence becomes less significant. 

HRRR grids, speeds, and colors at 8 AM for the resort region, resort circled

HRRR Gust Forecasts Surrounding Incident Time

The image below shows the HRRR Grid “blocks” with gusts colors and speeds without interpolation. The forecast was produced around midnight. The forecast is for 8AM. Resort is circled.

HRRR grib data over topo of region

HRRR Gust Forecast 12 Noon 

This forecast was produced at 11 AM for 12 Noon. A faint topo map is underlaid, as seen elevation interpolation/correction would be needed – see above. The top of the ropeway is circled. Speed forecasted without interpolation is around 55 mph.  

HREF gusts -60 hours

Ensemble Gust Forecasts 

With any forecast it’s important to examine if this was a “quick ramp-up” event, impossible to forecast or if there is model error. The general rule for accuracy is: same grid same speed in 3 consecutive hours equals high accuracy. The forecast chart below is an “ensemble” of 10 slightly different models called HREF High Resolution Ensemble Forecast. This model has been available since 2017. The forecast references every hour, 48 hours before the incident. HREF also must be interpolated. The gust chart was produced 60 hours before the incident. Speeds are +70 mph.

HREF gusts -56 hours

HREF 56 Hours Before Incident

Below is the HRF 56 hours before the morning of the incident, same “ramp-up” of wind with a little larger portion above 70 mph.

HREF gusts -39 hours

HREF - 39

Moving into a window of better accuracy, this chart was produced 39 hours before the 9AM opening showing speeds at 75 mph. 

HREF gusts -27 hours

HREF -27 

27 hours before the 9AM opening, speeds shown at 60 mph.

HREF gust forecast chart -3 hours before incident

HREF -3   

3 hours before the 9AM opening, speeds at 60 with some at 70 mph.

SPOTWX chart sample showing different wind selections

 Chart Option - Simple Line Graph

Those with challenges of color differentiation, the chart below covers the same HRRR model and produces a line graph of forecasts. Within that chart is the: model, elevation, time and 6 different wind forecasts. The sample chart below shows gusts in circles and is produced by SPOTWX.com. 

SPOTWX showing grid selections

SPOTWX - Grid Locator 

Grid locator is over the resort, different models with grid sizes are shown. 

Actual force vs wind speed

Wind Force vs Wind Speed

Wind Force is a much better example than speed for reactions with ropeways. Strictly speaking; gusts produce the wind force that can cause a derailment. Wind force and speed do not parallel each other. Looking at speed gauge can give you a false sense of security. 70mph=13lb/sqft     35mph=3lb/sqft 

Weather Summary 

48 hours before the incident: the gust arrival, duration and speed were characteristic of the forecast and did not significantly deviate in those 48 hours. 

The Structure of the Incident 

  • Based on tower adjustability, sheave stem clearance and the ropeway being load tested numerous times it is very likely there is nothing inherently wrong with the ropeway. 
  • The ropeway operated in a forecasted wind speed exceeding its design. 
  • It should be noted that the derailment was not the root of the incident it was one of many results.

 Potential Factors to the Incident 

  • The higher risk was not realized of operating a ropeway in a significant forecasted wind event.
  • An assumption that the NWS forecast applied to the resort is accurate.
  • A grid terrain and elevation correction to the weather model may not have been applied.
  • In 2011 this resort had a very similar incident. Insufficient corrective action normalized that event within the resort and with the industry. The persons involved in the incident described the wind coming in strong bursts…
  • Ropeway partners have not given enough attention to causal factors surrounding wind incidents. That lack of attention has been normalized.
  • Ropeway partners have not addressed forecasting skills in any reference handbook, standards, codes, or formal training. This has been normalized.
  • Ropeway partners have been lulled into a false sense of security with rope catcher performance. That high confidence has been normalized.
  • Misapplication of weather apps found on phones.
  • Misapplication of using wind speed gauges to forecast gusts.
  • Application of the wrong weather model.
  • The resort’s experienced technician may not have been available.
  • The resort may have been lulled into a false sense of security with updated rope catchers.
  • The resort’s personal may have formal risk training but it was not applied.
  • The resort’s personal may have formal forecast training but it was not applied.
  • Assumption that a “clear sky” indicates lower wind speed and less gusts.
  • Assumption that a ropeway (from stop switch activation to full stop) stop time will be quicker than the reactions from a gust.
  • Assumption that wind speed mirrors wind pressure.
  • Riding a ropeway in high wind can be very disconcerting. Consideration must also be given to rider comfort. 

  Wind Operation 

When operating in wind, the supervisor must take into consideration types of wind and its forces. There is intrenched old-timey thinking that you can reliably forecast gusts by steady-state wind speed. That thinking is not true. This is just one of the few reasons forecasters issue separate gust forecasts from steady-state wind. Gusts do not always mirror steady-state wind. Since predicting gusts from steady-state wind cannot-be-done, a forecast must be used. Past incidents have also shown gusts can force a rope from a sheave assembly while not running and gusts have forced riders from carriers.

  Recommendations

To the Industry

  • With public ropeway transportation, stress a higher level of care must be provided due to potential risk. With the difficulty of finding comparable ski resort activities as guidelines for higher care, one must use different industries. 
  • The industry must meet the demands needed to prevent the mistakes and omissions related to this incident. 
  • Reinforce the fact that gusts can be reliably forecasted and that the-rule-of-thumb of mirroring steady-state wind is wrong.
  • Reinforce the message that strength of gusts has caused full deropements and forced riders from carriers, operating on “slower” speed does not remove that risk. 
  • Have two identified technicians to be fully trained (designated responsible person) in running ropeways in high-risk weather. Designated “responsible persons” is not a new concept; accountants, bus drivers, first aid certified, explosives handlers, welders, NDT providers and rope splicers have similar designations at resorts.
  • Have two identified technicians to be fully trained in all ropeway aspects (see above).
  • Fully Trained: A developed curriculum, hands-on applications, verification of training, updated future training and verification.

Oversight agencies: 

  • Mandate the above training, apply corrective action if that practice is not implemented.
  • Contact similar oversight agencies and technicians with information gathered from this incident.
  • Make past key information readily available to technicians. 
  • With their broad base of experience, they should aim to bridge the gap with their knowledge in the missing portions of ropeway operation and reference standards.

Manufacturers

  • State in the service/operation manual and contact resorts directly: use gust forecasts at a tool for operational decisions.
  • With their broad base of experience, they should aim to bridge the gap with their knowledge in the missing portions of ropeway operation and reference standards.

Resort

  • It is never stated but Codes and Standards that apply to ropeways are minimum performance standards
  • Add a +3’ mast to the anemometer to prevent wind masking from the tower.
  • Back test and correlate forecasts with the actual wind at key locations.
  • Add wind “pressure” charts to all anemometer gauges.
  • Even if not mentioned in ANSI, USFS or insurance reference material: provide ropeway specific weather training to at least two technicians.
  • Dedicate a high-resolution monitor for forecast model viewing and have that monitor available to all responsible persons. 
  • Be aware of routine daily operation mindset, as every day will be different.

Summary

The normalization of deviance of this type of incident started many decades ago. Ropeway wind incidents causing damage and death is well documented. Early evidence this author found was a repair by Byron Riblet of a ropeway damaged by gusts in Oregon in 1898. Its quite possible the wrong chart and no consideration for corrections were used in the forecasts; this would have greatly reduced the forecast speed and timing. There are many ways to view a forecast. One does not need to be a meteorologist to establish a gust trend that morning. A simple line chart would show the trend that was to occur. Ropeway technicians cover two different roles in ropeway operation – they can be regarded as the mechanic and the pilot. As a pilot they must also have training in understanding severe weather. Currently, there is no requirement for formal training in ropeway operations and no free access to vetted ropeway information is available. At this point there is some truly tragic irony that ropeways are tested periodically but ropeway technicians are not.  Riding ropeways is a high-risk endeavor. Those risks have all been mitigated and with proper maintenance, no variables to higher risk will exist…with the exception of operations in wind. Accordingly, one needs to take the steps to understand the risk and then apply that knowledge to daily ropeway operations.

  The risk can be evaluated by the TREE principle: Technician, Ropeway, Environment, External Factors

  • Technician: Level of operational and weather forecast experience
  • Ropeway: Performance characteristics in wind
  • Environment: Current and forecasted weather
  • External Factors: Opening of a high use ropeway, supporting ticket sales, unknowledgeable directors

A review can then be used to show what factors are applied to establish a level of risk for that circumstance and what factors could be changed to lower that risk. 

There is an old saying that rings true with ropeways – Everything Matters. You must employ all safeguards with every detail of ropeway operation because ultimately it serves the public.

  References:

  Analytical Review of Ropeways - Gottfried Hofmann

ANSI “B77” - Ropeway Standards

CalTOPO – Mapping Toolkit

FAA – Risk Management

Grid Overlays – NOAA Grid Toolkit, Google Earth

HRRR – NOAA Global Systems Laboratory, Ventusky, Utah University HRRR archive, Mesowest

HREF – NOAA Storm Prediction Center

LMOE - Regional ropeway discussions

MetED - Comet Weather Training

NCEP – Chart Tool

NWS – Daily forecasts

OITAF NAC – International ropeway discussions

OSHA – Risk Management

PNSAA – Regional ropeway discussions

Society of Ropeway Technicians SORT – Internal data: training and incidents

SPOTWX – Model grid forecast line charts

USFS – Manual 7300 Chapter 7320

Ventusky - Grid, Number, Color charts

WunderGround – Surface chart archive


  

This report does not cover: carrier swing dynamics, catenary curve, force diagrams, local terrain flow, passenger area, profile angle, rope tension factors, sheave liner wear, span swing characteristics, tower load, wind pressure correction factors – it is assumed a combination of factors are well past their limits when a rope derails…


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  • Montana Incident Report
  • Montana Incident Page 2
  • Who We Are - What We Do
  • Incident Notes
  • SORT Discussions

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