 When weather or extremely high demand for a certain airport or airspace becomes a factor, there may be ground "stops" (or "slot delays") or re-routes may be necessary to ensure the system does not get overloaded.The primary responsibility of clearance delivery is to ensure that the aircraft have the correct aerodrome information, such as weather and airport conditions, the correct route after departure and time restrictions relating to that flight.This information is also coordinated with the relevant radar center or flow control unit and ground control in order to ensure that the aircraft reaches the runway in time to meet the time restriction provided by the relevant unit.