AERODROME CONTROL TOWER

        Aerodrome control towers shall issue information and clearances to aircraft under their control to achieve a safe, orderly and expeditious flow of air traffic on and in the vicinity of an aerodrome with the object of preventing collision(s) between:
 a) aircraft flying within the designated area of responsibility of the control tower, including the               aerodrome traffic circuits;
 b) aircraft operating on the manoeuvring area;
 c) aircraft landing and taking off;
 d) aircraft and vehicles operating on the manoeuvring area;
 e) aircraft on the manoeuvring area and obstructions on that area.
        Aerodrome controllers shall maintain a continuous watch on all flight operations on and in the vicinity oF an aerodrome as well as vehicles and personnel on the manoeuvring area. Watch shall be maintained by visual observation, augmented in low visibility conditions by an ATS surveillance system when available. Traffic shall be controlled in accordance with the procedures set forth herein and all applicable traffic rules specified by the appropriate ATS authority. If there are other aerodromes within a control zone, traffic at all aerodromes within such a zone shall be
coordinated so that traffic circuits do not conflict.
        The functions of an aerodrome control tower may be performed by different control or working positions, such as:
 a) aerodrome controller, normally responsible for operations on the runway and aircraft flying                 within the area or responsibility of the aerodrome control tower;
 b) ground controller, normally responsible for traffic on the manoeuvring area with the exception of       runways;
 c) clearance delivery position, normally responsible for delivery of start-up and ATC clearances to         departing IFR flights

(DOC 4444,CHAPTER 7)