may work if they return to their previous unit/sector, but an experienced ATCO going to a busy new unit will take around a year to qualify and many years to be experienced. You can’t just switch on the taps and train all of the shortfall either only one trainee at a time can be in position and the qualified ATCOs also need to have a go sometimes to keep their recency. A 10% staff shortfall could take a year or two to replace even using experience trainees. If we’re looking at traffic returning towards capacity then we’d better start recruiting now before redundancies have even been “offered”. Most ATC units were quite short-staffed before COVID19, relying on overtime to make up the shortfall. See also units with a change of ANSP contract taking years to return to safe staffing levels. NATS also has a retirement bulge looming in part caused by a historic short-sighted staffing cycles.