How to safely shorten your tether
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At a busy anchor, especially when you have some distractions, it's quite easy to clip your rappel tether / PAS incorrectly.
I’ve done this myself, and fortunately realized my mistake very soon after, yikes!
The main cause of this problem is often when changing the length of your tether.
A common way to do this is to completely unclip the carabiner from one loop, and then clip it into another.
When you do this, you introduce the chance of clipping it wrong.
Here are two recent accidents where this seemed to be a direct cause. (Both of these reports are from the American Alpine Club’s website called The Prescription, which offers a monthly blog and archive of North American climbing accidents.)
Here's the analysis of one accident from the American Alpine Club:
Laycock’s accident was eerily similar to another recent incident, suffered by a climber in Arizona. Both fallen climbers had tied overhand knots in a 120cm length loop of 20mm sewn webbing to create adjustment pockets for a home-made PAS. This is a common practice. In both cases, it appears that the tether was not clipped correctly with the carabiner, but instead the knot caught in the bottom, non-gated end of the tether carabiner.
Wow, that photo is scary! You can see that clipped like this the knot MAY jam into the carabiner temporarily, even under light bodyweight. This could easily fool you that you are properly connected, when in fact you're absolutely not!
