top of page



Date of Incident





Sport rock climbing


Re-Threading Belay


Serious injury requiring medical treatment


Three climbers who all had previous outdoor sport climbing experience were climbing in a group. Due to one climber (Climber B) having less experience than the others, Climber A led the route first, placing opposed quickdraws on the anchor bolts to lower off. Climber B then led the route and used the in situ quickdraws to lower. Finally Climber C led the route with the intention of cleaning the anchors and lowering off the fixed gear.

Climber C reached the anchor, which was situated on a large, sloping ledge (approximately 4-5 metres above the highest bolt on the route) and shared with an adjacent route. The climber was using a knotted sling and screw gate carabiner as a safety system, and as the anchor was positioned above head height, had to reposition the screw gate on the knotted sling to allow it to reach the anchor, which required the screw gate to be taken off the sling and reattached. The screw gate was attached to the anchor and locked (confirmed later when gear was retrieved). The climber weight tested the sling then indicated they were safe to the belayer (who kept the climber on belay), before removing the quickdraws from the anchor. Upon leaning back to attach the quickdraws to their harness, the sling released from the screw gate and Climber C stumbled backwards and fell approximately 10-12m down the series of ledges on the climb. The fall was arrested by the belayer approximately 1 metre above the ground. Bystanders assisted the other two climbers in administering first aid and calling the emergency services. The fallen climber was attended by paramedics and transferred to Glan Clwyd A&E by ambulance. After a full body CT scan, the climber was confirmed to have no broken bones but suffered cuts/abrasions, very severe bruising, whiplash and a sprained ankle.


The key learning point is to always have redundancy in your safety system!

The incident occurred when using a large width sling (approximately 20mm width) which when knotted creates knots which are large enough to “catch” in the narrow end of a standard sized locking carabiner. When this occurs it is possible to pull the sling sharply downwards (tested at the scene with the help of bystanders who assisted) without dislodging the knot, however, when the knot is pulled outwards, it easily dislodges as happened when the climber twisted to attach the quickdraws from the anchor to their harness. The sling was still intact and attached to the climber’s harness after the fall while the screw gate was locked and attached to the anchor.

The rethreading technique the climber had been taught, and had used many times before without incident, was to attach to the anchor via a sling, then pull up slack on the rope and attach the rope to a gear loop via an overhand knot and screw gate to prevent dropping it. The figure of 8 knot is then untied from the harness, threaded through the belay and retied to the harness before transferring the climber’s weight back to the rope/belayer and removing the sling. This method is still widely used and some climbers will even have their belayer take them off belay during this process. Had this occurred here or the fall occurred after slack had been pulled up, a ground fall would have been inevitable. The key flaw in this system is the lack of redundancy; the climber is entirely reliant on the sling to prevent a fall while retying.

There are several ways this method can be improved:
• Clip to the anchor using a quickdraw and then the sling (prevents a large fall from anchors when clipping the sling or if the sling fails)
• Tie a second knot in the rope and attach to a load-bearing part of the harness (e.g. belay loop) BEFORE untying and rethreading the original knot. The second knot is then untied prior to lowering.
OR retie on a bight which has been threaded through the anchor before untying the original knot (arguably simpler but leaves a long tail so can’t be used when the length of the rope is only slightly longer than required for the climb and requires anchor to accommodate a bight passing through).
• Climber should not be taken off belay
• Use of a personal anchor system rather than sling (can be made at home using a length of climbing rope) as this is dynamic and there is no chance of a knot catching in the carabiner and appearing attached when it is not.


Slip, trip or fall, Climber Error



Reported By


Wearing Helmets?


Rescue Services Involved?



14 August 2019 at 15:46:24

For more advice and guidance on good practices visit BMC skills

All reports are self-submitted and have not been edited by the BMC in any way, so please keep an open mind regarding the lessons and causes of each incident or near-miss. 

If you have a concern regarding this report please contact us at

bottom of page