Air Traffic Services and Airspace
Services and airspace
ICAO Annex 11 covers ATS: area control, approach and aerodrome control. Annex 10 covers communications, navigation and surveillance. Airspace is classified A-G, with different rules for IFR/VFR, separation and clearances. Class A is IFR only; Class C mixes IFR and VFR with separation; Class G is uncontrolled. Know the services: flight information service (FIS), alerting service and air traffic control service.
Clearances and separation
An ATC clearance is an authorisation, not a guarantee of safety; the pilot remains responsible for terrain clearance and collision avoidance. Separation minima depend on radar/non-radar and airspace. Readback requirements for clearances are frequently tested.
Traps
- Assuming a clearance removes pilot responsibility.
- Confusing FIS (information) with ATC (separation).
- Misclassifying airspace classes and their VFR/IFR allowances.
- Forgetting that class G has no ATC service and no separation.
Worked example
A VFR flight in Class C airspace: VFR is permitted but IFR/VFR separation is provided, and a clearance is required. In Class G, no clearance is required and no separation is provided; the pilot is responsible for see-and-avoid.
Rule of thumb
Clearance = permission; separation = service; see-and-avoid = always the pilot's duty.