This is not BAA but EU regulation. And yes there is flexiblity. Slots are only lost when the airline uses them for less than 80% of the time, so there is automatic 20% flexibility. In addition, there are additional special circumstances when an airline can keep its slots if it has used them less than 80% of the time (grounding of aircraft type normally used for the service, closure of airport or airspace, serious disturbances at the relevant airport, etc...). A 'few months' woudl bring you almost to the whole seasons, and slots are allocated by season (winter and summer). Don't forget that slot control only happens at heavily congested airports where there is a major mismatch between supply and demand. An unused slot for several months is one that could usefully be used to provide another service. IMO, it would be open to a slot co-ordinator to reclaim slots from an airline which misuses its slots. Slots allocated for a scheduled air service can be reclaimed by the co-ordinator and returned to the pool for the next season if "the air carrier cannot demonstrate to the satisfaction of the coordinator that they have been operated, as cleared by the coordinator, by that air carrier for at least 80 % of the time during the scheduling period for which they have been allocated." Using slots originally allocated for a scheduled air service simply for slot nursing and not for providing a scheduled service is arguably not 'operated as cleared by the coordinator'.