grandfather rights
From Longman Business Dictionarygrandfather rightsˈgrandfather ˌrights [plural]TRANSPORT at an airport, the rights of AIRLINEs to use TAKE-OFF and LANDING SLOTS (=times at which aircraft can leave and arrive) that they have always had, and not to be forced to give or sell them to other airlinesAt present, airlines hold the slots in perpetuity (=for ever) giving them so-called grandfather rights. → right