This is a two pitch route, if you haven't done it, get on it, it is one of the best routes in the country; I almost fell off laughing). The mid height belay is formed by a constricted stance (when you have 3 people) on top of a chock stone at the front of a cave. I led the first pitch and being out of slings built the 3-point anchor with the ropes. In order to make the stance more readable (which given what happen is somewhat comic) and easier, when the second (Pete) arrived I rebuilt the belay using slings he had cleaned to facilitate tying 3 climbers into a powerpoint and swapping ends of the rope so Pete could lead the final pitch.
The third arrived and clipped into the powerpoint. The stance is constricted, the cave and powerpoint dark, the light from month of the cave bright. Pete is tied in with a rope, I'm tied in with both ropes, the third is tied in with one rope. Pete went to clip directly into the powerpoint with a daisy (PAS-style). This was difficult for him as the powerpoint was below him and out of sight, it was also under a mess of other ropes tying us in, or going from me to the anchor pieces. Given this difficultly I grabbed the PAS and clipped Pete into the powerpoint. A while later Pete found his PAS was not clipped to the power point, yet its twist lock carabiner was. And hence he was probably not tied to the cliff (assuming at this point he had untied his first attachment point, I can't remember). Falling off the chockstone would be fatal.
The belay at that point was visually complex. This should not have been a problem. We were all experienced. The light was difficult. I took Pete's PAS without realising he keeps it stored in a different way than most climbers: rather than keeping the twist lock on the end (possibly with a keeper), he keeps it attached to the middle. This and the fact that I was using someone else's kit to secure someone other than me should have made me run a double check, especially as I was clipping him to the back of the powerpoint and hence operating by feel not sight. I opened the gate and the gate snapped back shut. Except in that half a second the PAS jumped out of the gate. I checked the twist lock was done up. I checked the twist lock was in the powerpoint. I didn't check the PAS was still in the twist lock, nor perform an alternative inspection by giving the PAS a yank. Because the powerpoint was being squashed against the rock, the PAS was held in place by being trapped between the powerpoint and the chockstone, so this issue was not spotted.
I would not normally do such a second test, but then I would not normally be operating out of sight, with three people on top of each other, in a cave with a blinding light in my face meaning my vision was poor. Nor using someone else's kit to secure someone else. I should have triple checked.
Interestingly, Pete failed to secure himself to a route in Norway with the same PAS. So this keeps happening to him. In that instance, the PAS got entwined with a big sling, and it was the locker on the sling that he clipped to the anchor, rather than one on the PAS - he had used that one at some other point on the climb for something else. Two data points don't make a conclusion, but I am left wondering if one should consider always keeping the locker on the end of the daisy, shortening it by other means, and consider using a retainer on said locker - many do just that.
Trad rock climbing
Unclear thinking and a failure to check the anchor
Rescue Services Involved?