Unsecured grip causes chairlift to slide backwards on an incline

Incident overview

A grip of a detachable chairlift failed to clamp on the rope securely. As the chair being transported along the main cable came to a steep incline, it slid backwards along the cable.

Regulated industry sector

Passenger Ropeway – Above surface ropeway

Location

Sun Peaks

Investigation conclusions

Site, system and components

High speed chairlifts detach each chair from the main cable when they are at loading and unloading stations. This allows for easier, safe and efficient loading and unloading. The grip is the device on the carrier (chair) that attaches to the main cable. A detachable grip is designed to be opened (detached) and closed (attached) upon entry/exit of a station. It has multiple components in order for this action. Grips on passenger ropeways are subject to dynamic stress. Therefore, according to regulations and manufacture requirements grips need to be completely stripped down and inspected on a pre-determined cycle.

Failure scenario(s)

A fastening element in the detachable grip was missed during the re-assembly of the grip. As the grip cycles through the load and unload stations a component in the grip that wasn’t  firmly secured became loose and  interfered with the closing (attaching on the main cable) action of the grip.

Facts and evidence

As reported by passengers on chair behind:

• Mid-way up lift line chair ahead slid back hitting their chair
• Had to move out of way in seats to prevent from getting hit
• Chairlift did not stop
• Two chairs entangled together and continued moving uphill
• At the top (unload) station yelled at operator to stop lift

As reported by the Operators:

• No stop faults indicated as grip was moving through load station
• Correct spacing between chairs when they left the load station
• Top (unload) operator noticed the two chairs together as they came over the last tower
• No sign of grip slippage (spacing issues) prior to incident

As reported by the Duty Holder:

• Mechanical issue with the grip
• Grip was last rebuilt Dec. 25, 2017
• Grips are built and checked for completeness by the same mechanic
• Grips are inspected, tested and rebuilt during full operation season

As reported by the mechanic who assembled the grip:

• Commonly interrupted during assembling of grip for other chairlift operation issues

Causes and contributing factors

It is likely that the mechanic rebuilding the grip missed a securing element, resulting in a component inside the grip blocking the attachment procedure of the grip on the main cable. The mechanic being interrupted during the grip rebuild process, along with the quality control being completed by the same mechanic who built the grip are contributing factors.

Impact

• Injury
  • Qty injuries: None
  • Injury description: None
  • Injury rating: None

Damage

• Damage description: Insignificant marking of chair and carrier components
• Damage rating: Insignificant
• Incident rating: Insignificant