Granby Ranch HSQ Accident Report

TomWhiteTomWhite advanced
in NELSAP Forum Posts: 404
I'm amazed at what can (or did) go wrong with a HSQ.

Granby Ranch Investigation
Report Released

May 11, 2017 Peter
Landsman
1

 

The
Quickdraw lift at Granby Ranch, Colorado is a 1999 Leitner detachable quad
where a “rare dynamic event” last December caused a a chair to contact
this tower, killing one and injuring two children.

 

The
Colorado Passenger Tramway Safety Board released its 151-page final report on last December’s fatal accident at Granby Ranch this afternoon.
 The investigative team included seven professional engineers with
more than 250 years of combined lift experience with support
from Leitner-Poma and Granby Ranch personnel, among others. The team
conducted extensive tests on the Quickdraw lift from the afternoon of the
accident through January 5th and spent months writing this detailed
analysis, identifying contributing factors and making recommendations for
changes.  Appendices include witness statements, photographs and prior
inspection reports but the core of the document is 13 pages which everyone
who works on ski lifts should read.  I’ve done my best to summarize
below.

 

Chair 58 contacted tower 5 at a 40-degree angle that
morning due to two contributing factors.  The first was the
tuning of a new drive installed last Fall by an independent
contractor.  Two specific parameters may have created pulses of
energy and rope instability, the report notes.  “It is probable that the
combined effect of [these two settings] 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 second contributing factor was the
influence of one or more speed changes leading up to the incident.

Other potential contributing factors were:


  • Control system
    complexity resulting from the new ABB DCS800 drive’s interface with older
    Pilz/Leitner low-voltage controls.

  • A control board
    replacement from February 2016.

  • Possible damage
    to the electric motor encoder.

  • Unknown
    electrical cycle shown in data logs that had occurred at a 3.7 second
    interval over the entire life of the lift.

  • Tension
    factor(s) that would require more testing to determine.

  • Natural
    instability of the profile.  “There appears to have been a very
    unique combination of rope tension, carrier spacing, tower spans, tower
    height, carrier loading and natural carrier movement that led to the
    transverse carrier swing that resulted in Carrier 58 hitting Tower 5,” the
    document states.

  • Natural harmonic
    response of the haul rope.

Wind
was not found to be an outside influence, nor was passenger conduct.  “The
incident that occurred on December 29th, 2016 at Granby Ranch was unprecedented,”
the investigative team wrote.  “Although many factors may have combined to
amplify the effect of the rope instability leading to Carrier 58 colliding with
Tower 5, the performance of the new drive is considered to be the primary cause
of the incident.”  The report explains electronic drives such as the
DCS800 added to Quickdraw last year and used on many lifts are also
used in a wide variety of other applications.  The tuning and
“fine-tuning” of a drive is complex and unique to each application and lift.
 “It appears the new drive was not comprehensively tuned to this
particular lift during installation,” the document says.

https://liftblog.com/

Comments

  • mapnutmapnut expert
    Posts: 772
    Ugh, that's worrisome. Sounds like a design flaw that wasn't readily evident. Could there be similar accidents waiting to happen?
  • joshua_segaljoshua_segal expert
    Posts: 1,671
    mapnut said:

    Ugh, that's worrisome. Sounds like a design flaw that wasn't readily evident. Could there be similar accidents waiting to happen?

    At Temple Mtn. back in 1984-5, one tower, which was correctly shown on the plans, was incorrectly installed. As a result, the tower was not damping out an harmonic resonance.  It de-roped two days in a row, (one day I was evacuated and one day, I was on the team helping with the evacuation.)  To get through the rest of the season, they filled the tower with concrete.  That damped out the resonance and it did not de-rope again that season.  The tower was replaced correctly over the next summer.  That old tower sat in the parking lot for years.  I have no idea either how they got it to the parking lot or how it was finally removed.  With all that concrete, it weighed tons!
  • rickbolgerrickbolger expert
    Posts: 1,028
    Thanks for posting
  • lotsoskiinglotsoskiing expert
    Posts: 634
    So the rope was shaking so badly that when the chair went by the tower it slammed into it, causing it to fall or the kids to be ejected? Trying to visualize this. Is the lift's 'harmonic resonance' the same phenomenon that took down the bridge over the Tacoma Narrows (Galloping Gertie)? Was the cable bouncing up and down or laterally?
  • obienickobienick expert
    edited May 15 Posts: 823
    I read it as the rope was causing the chair to sway left/right and the chair hitting the tower caused the family to be ejected.  It says the chair was at a 40° angle when it hit the tower. 
  • bobbuttsbobbutts intermediate
    Posts: 92
    It seems so strange that it would run normally for some time and then just one chair swung so extremely to collide with the tower.  Did other chairs on this lift exhibit this behavior to a lesser degree too before the catastrophe?

  • rickbolgerrickbolger expert
    Posts: 1,028
    bobbutts said:

    It seems so strange that it would run normally for some time and then just one chair swung so extremely to collide with the tower.  Did other chairs on this lift exhibit this behavior to a lesser degree too before the catastrophe?

    according to the report and witness' statements, yes it affected other chairs
  • TomWhiteTomWhite advanced
    Posts: 404
  • lotsoskiinglotsoskiing expert
    Posts: 634
    No indication of whether they had the safety bar down. Seems that might have kept them in and/or given them something to hold on to. Very sad story nonetheless.
  • LiftGuyLiftGuy advanced
    Posts: 125
    mapnut said:

    Ugh, that's worrisome. Sounds like a design flaw that wasn't readily evident. Could there be similar accidents waiting to happen?

    Chair 58 contacted tower 5 at a 40-degree angle that
    morning due to two contributing factors.  The first was the
    tuning of a new drive installed last Fall by an independent
    contractor.  Two specific parameters may have created pulses of
    energy and rope instability, the report notes.  “It is probable that the
    combined effect of [these two settings] 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 second contributing factor was the
    influence of one or more speed changes leading up to the incident.

    Neither of these factors were "design flaws". They were flaws in the drive modification that was installed by a third party contractor. The 'fine tuning' of the drive parameters and the lack of a timer for the slow circuit are described further in the first 13 pages of the report.
    On you question about the restraint bar- eye witness reports were that the bar was not down. As you say, a very sad story.
  • TomWhiteTomWhite advanced
    Posts: 404

    Colorado officials propose changes to ski lift
    systems

    System could be required at all resorts in
    state

    By Associated Press | Wednesday, May 17, 2017 2:06 PM

     

    Associated Press file

    Officials are looking
    to implement a system that would create a delay between when lift operators
    slow and accelerate a chairlift’s speed after a woman died in December after
    falling from a chairlift.

    DENVER – Colorado officials are recommending safety changes to
    ski lift systems statewide following the death of a woman.

    Colorado’s chief chairlift inspector Larry Smith told The Denver
    Post Monday that the upcoming changes to chairlifts will be small but will
    improve safety.

    The move follows the death of a Texas mother who died last
    December after falling from a chairlift. Kelly Huber and her two daughters fell
    from the chair after they hit a tower.

    Officials are looking to implement a system that would create a
    delay between when lift operators slow and accelerate a chairlift’s speed. They
    believe the change will reduce the chairs’ movement. The Colorado Passenger
    Tramway Safety Board is considering making the delay system a requirement.

  • lotsoskiinglotsoskiing expert
    Posts: 634
    And/or require safety bar use. 

    I know this will ignite a storm about relative safety with safety bars down (I have heard all the arguments, from both westerners (where many lifts have no safety bars) and easterner libertarians who adhere the 'live free or die' ethos when it comes to this sort of thing (and bike helmets and seat belts...), but I know it is a hell of a lot harder to fall out of a chair with the bar down than without. May not have saved this family but then again it might have...

    Will don my hard hat now, because I choose to, not because someone is making me do it
    :-??
  • rickbolgerrickbolger expert
    edited May 19 Posts: 1,028

    And/or require safety bar use. 

    +1 Except on that black chair at Magic

    When people piss and moan about putting the bar down, I say, yeah I don't like seat belts or smoke alarms...but I use 'em.

    And -- not to dishonor this mom, according to the patroller on the following chair she did protect and probably saved the life of her youngest on the way down -- I'm willing to bet she always made her kids wear bike helmets.  I know they wore ski helmets.  But eschewed the safety bar.  Puzzling...and sad.
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