One of the big things that I don't agree with in DIR is the refusal to use 2 wings, or a dual bladdered wing. I can understand that if your drysuit can make you neutral or even slightly positive, even if grossley over-inflated, then that could count as redundant buoyancy. However, if you are using large twinsets and/or several stages filled with nitrogen based gas, I'm sure that a situation culd occur where a drysuit by itself will not be able to offsett the negative buoyancy of the gas in the cylinders. I know that below 30m GUE use helium which reduces the weight of the gas, but I think a long 30m dive (maybe in a cave?) with, say, twin 12s and a couple of al80 stages is quite conceivable. The other scenario could be diving in a wetsuit with a twinset. Obviously it is important to be correctly weighted, but even so, a full twinset alone without stages is over 6kg in negative buoyancy, and this will increase as you descend with compression of the wetsuit. If your wing were to have a complete failure, such as the inflator hose disconnecting from the wing, then I don't see how you could safely achieve neutral buoyancy and complete any decompression necessary. The solutions that I came up with without using a second bladder were to, a) not dive in a wetsuit with twins, and, b) if you have a wing failure immediatly hand off any stages to team members and they could lift you if necessary. As for "a", diving in a wetsuit is so nice compared to a drysuit, if I was somewhere nice and warm I'd want to be a wetsuit if possible, so I don't think I'd be too happy with that. For "b", this seems like a reasonable solution, making the most of your team to help you overcome a problem so you don't need extra kit, but in either of the 2 scenarios mentioned above, you have no back-up adjustable buoyancy source, and while I appreciate that you don't need to have too much redundancy, to not have a plan B that you could execute yourself regarding a buoyancy failure seems a bit dodgey to me. Can an extra inflator hose over your right shoulder cause that much bother? Or am I just missing other obvious solutions that negate the need for a second wing?