The problem is the gate agents don't understand that CASS stands for "COCKPIT ACCESS" not cabin access. CASS is only required for offline use so if you are riding on your own metal, or codeshare you should not need a passport (unless they use CASS for all cockpit access like Delta, or FedEx). Exp96 is correct in saying that passports are no longer required by TSA. The picture displaced the passport requirement in September of 2006. The problem is that all airlines who became CASS participants prior to the picture requirement had a passport requirement in their Ops Specs. Some are going back and getting it removed, and I think most of those participating after the picture requirement are not even entering it into their Ops Specs.....therein lies the discontinuity.

Bottom line........always carry your passport with you if jumpseating is anticipated.