FULL STORY: Electrical drive blamed for chairlift fatality
State officials reported that an electronic drive control was cause for the December chairlift fatality at Ski Granby Ranch, according to a report released late last week.
The Colorado Passenger Tramway Safety Board released its report Thursday afternoon that detailed findings of the months-long investigation into the incident on the Quickdraw Express that ultimately claimed the life of Texas resident Kelly Huber.
The 151-page report, of which 138 pages are appendices, was complied over a period of roughly three months. While the heavily technical report laid out the cause of the incident, it stops short of placing direct blame on any specific party.
Huber and her two daughters fell from the resort’s Quickdraw chairlift Dec. 29. Huber, 40, succumbed to a ruptured aorta caused by the blunt force trauma of the fall, while her two daughters, ages nine and 12, sustained non-fatal injuries.
Granby Ranch CEO Melissa Cipriani released a statement to Sky-Hi News on Sunday that indicated the resort was reviewing the report.
“This is a 151-page report that deserves careful review,” Cipriani stated. “Granby Ranch continues to comply to all tramway board directives.”
She concluded the statement by offering condolences to the Huber family and stressed the resort’s commitment to the “health and safety of its guests.”
Drive system at fault
Findings and eyewitness accounts led investigators to believe that the performance of the new drive system was the primary cause of the incident, according to the report.
The drive system is the machine that moves the “rope,” or cable, along the mountain.
“It is the conclusion of the investigation team that the selected tuning of the drive, combined with the natural harmonics of the lift system, along with rapid speed changes, caused the rope instability,” the report indicated.
The report went on to assert that the new drive system was not “comprehensively tuned” to the particular lift during its installation.
Electrical controls for the Quickdraw were modified in early December, according to the report. Ski Granby Ranch had submitted all required documents for modification of the new drive, a board inspector tested the lift modifications in early December and the lift was licensed on Dec. 15. During multiple acceleration tests, neither the inspector nor any of the personnel who witnessed the test reported any unusual rope dynamics, the report stated.
“The investigation team remains steadfast in its opinion that the existing configuration of the electronic drive and the original, pre-modified, low-voltage control system were unsafe for public operation,” according to the report.
One day prior to the report’s release, the Colorado Passenger Tramway Safety Board had tabled further action on the incident, forwarding the matter to the state’s Office of Investigations for potential disciplinary action.
An event like none other
Investigators noted the unprecedented nature of the event throughout the report.
“No one on the investigative team has ever witnessed or heard of a similar event,” investigators stated. “Likewise, literature does not describe such an event.”
In eliminating potential causes, investigators found there was no passenger misconduct nor were weather conditions unfavorable.
A statement released by Cipriani in mid-January, in the investigation’s early stages, indicated that the lift had been operating safely since its installation 16 years ago and “up until an independent contractor made modifications to the lift’s electrical drive/control system before the start of the current season.”
Cipriani indicated in the statement that preliminary investigation had revealed the cause to be the independent contractor’s modification of the lift’s electrical drive/control system.
Though investigators identified two contributing factors: drive modification and influence of speed changes.
It was confirmed by the report that the lift’s drive parameters might have created pulses of energy that could explain rope instability.
“It is probable that the combined effect … may have resulted in the drive trying to respond too aggressively to lift demands when changing from fast to slow and back to fast again,” the report stated.
Such unstable lift dynamics could only be re-created by making rapid changes in lift speed with the newly installed drive, according to the report.
Several witness statements included in the report reported multiple changes in the lift’s speed just prior to the incident.
For future safety
Investigators suggested Ski Granby Ranch employ a series of 10 action items, above and beyond current national and industry safety standards to ensure public safety in the future.
Among the suggestions were installation of speed change time delays, stop time delays, analog drive modifications and installation of a “black box” on all aerial lifts that collects data on starts, stops, speed changes and other parameters affecting lift cable dynamics.
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