Air Traffic Services Rules and Procedures
The three services
ATS comprises air traffic control, flight information service and alerting service. Know what each provides and its boundaries. ATC has three functions: area control, approach control and aerodrome control. The controller issues instructions, which are mandatory and require readback, while information is advisory. Clearances are limited to traffic separation and are not authority to violate regulations.
Control positions and coordination
The tower controls the aerodrome traffic circuit and runway; approach handles arriving and departing controlled flights; area control handles the en-route phase. Transfer of control and transfer of communication must be coordinated, and the accepting unit assumes responsibility only when the prescribed conditions are met. Know the priority rules: distress, urgency, then other traffic, with special handling for medical and head-of-state flights.
Traps in questions
A frequent trap is confusing transfer of control with transfer of communication, or assuming that a clearance cancels the pilot's responsibility for terrain clearance under IFR. Another is treating flight information service as a separation service. Questions also probe when a controller may issue a clearance that deviates from a published route.
Rule of thumb
Use the sequence: identify the service, identify who has responsibility, then identify the condition for transfer. Worked example: an aircraft is cleared to enter the control zone. The tower has control of the aerodrome traffic; separation from other circuit traffic becomes the tower's responsibility once the aircraft enters the tower's area of responsibility, and coordination must confirm the boundary point.