I wonder how many vacant shifts there are on the CNS APP roster in December. It's likely that tonight's TIBA/TRA is because no-one was rostered on the shift (or shifts), and no-one agreed to cover the shift on Overtime. An audit of vacant shifts on rosters across the country would probably reveal frighteningly high numbers, with the expectation that someone agrees to cover the shifts either by Change of Shift, extending their shift or working Overtime. If not, then TIBA/TRA, or OPR Restrictions (see other thread).