Tutorial: ATC Guide - Device Failure Modes, The Ones You Don’t Know About

Photo by: Taren Maroun
Climber: Tony Lima

Autoblocking devices like the Petzl Reverso and Black Diamond ATC Guide have become a standard in multi-pitch climbing. They’re used to belay a ‘second’ or follower, from above and are often used ‘hands free.’ When set up correctly they are mostly reliable, but they have potentially fatal modes of failure that you need to be aware of.

Break Strand Jam/Flip

When belaying in guide mode, on a single rope, of thin diameter, the break strand and load strands can pass each other, jamming or even defeating the device and leading to an uncontrolled fall. Prevent this catastrophe by tying periodic backup knots on the break strand.

One Handed Clove (Accidental LSD)

Securing the second to the anchor with a one handed clove hitch on the load strand renders the device temporarily vulnerable. If the second falls mid-process, the carabiner will redirect the load strand, defeating the autoblock device and leading to an uncontrolled fall. Avoid the issue by using the break strand to secure the second or by completing the clove in the air before clipping the anchor.

Different Diameters

Belaying two followers in guide mode on ropes of different diameters can permit slippage on the thinner line. Manage the issue with backup knots on the break strand of the thinner line.

Multidirectional Load

Belaying two followers in guide mode when the route traverses horizontally from directional protection to the anchor, creates inapparent danger. When both followers are clipped to the directional, they are safe. BUT!! if one remains clipped with a horizontal direction of pull and the other is below the plaquette with a vertical direction of pull the plaquette will not engage. If the followers weight the rope in different directions, there will be one or possibly two uncontrolled falls. Prevent catastrophe by tying occasional backup knots on the break strand.

awkward To help avoid the issue, make sure the second connects with their personal anchor or with a clove (in the air) on their load strand to avoid weighting the belay device and help protect the third.

Using frequent or even ocasional backup knots on the break strand would prevent catastrophe for all of these failure modes and should be adopted as a habitual standard of practice. Tie them intermittently and any time you’re going hands free. A simple overhand on a bight is best. I prefer to use a slip knot which is less secure, but quicker to tie and untie. Tie off with a proper mule overhand to secure the device if leaving the device unattended.