Airspace classes A to G — and how they apply in the Tehran FIR

Why airspace is classified

ICAO Annex 11 divides air traffic services airspace into seven classes, A to G. The class tells a pilot, before take-off, which flights are allowed, whether an ATC clearance is needed, who is separated from whom and what service to expect. Classes A to E are controlled airspace; F and G are uncontrolled.

A State chooses which classes it uses and publishes them in its AIP (ENR 1.4 and ENR 2.1, and AD 2.17 for each aerodrome). The same area can have different classes at different levels.

The seven classes

• Class A — IFR flights only. All flights receive air traffic control service and are separated from each other. VFR is not permitted.
• Class B — IFR and VFR. All flights receive ATC service and are separated from each other.
• Class C — IFR and VFR. IFR flights are separated from IFR and VFR flights; VFR flights are separated from IFR flights and receive traffic information on other VFR flights.
• Class D — IFR and VFR. IFR flights are separated from other IFR flights and receive traffic information on VFR flights; VFR flights receive traffic information on all other flights.
• Class E — IFR and VFR. IFR flights receive ATC service and are separated from other IFR flights; VFR flights do not need a clearance and receive traffic information as far as practicable. Class E is not used for control zones.
• Class F — IFR and VFR. IFR flights receive an air traffic advisory service; all flights receive flight information service on request.
• Class G — IFR and VFR. Flight information service on request; no ATC clearance and no separation service.

Clearance, radio and speed

• An ATC clearance is required for every flight in classes A, B, C and D, and for IFR flights in class E.
• Continuous two-way radio communication is required in classes A to D, and for IFR flights in classes E, F and G.
• Below 10 000 ft AMSL a 250 kt IAS speed limit applies to VFR flights in classes C to G and to IFR flights in classes D to G, unless the State approves otherwise.

VMC visibility and distance from cloud (Annex 2, Table 3-1)

• At and above 10 000 ft AMSL (classes B to G): flight visibility 8 km; 1 500 m horizontally and 1 000 ft vertically from cloud.
• Below 10 000 ft AMSL and above 3 000 ft AMSL or 1 000 ft above terrain, whichever is higher (classes B to G): flight visibility 5 km; 1 500 m horizontally and 1 000 ft vertically from cloud.
• At and below 3 000 ft AMSL or 1 000 ft above terrain — classes B to E: flight visibility 5 km; 1 500 m horizontally and 1 000 ft vertically from cloud. Classes F and G: flight visibility 5 km, clear of cloud and with the surface in sight (States may allow lower visibility for slow aircraft).
• Class A has no VMC minima because VFR flight is not permitted.

How Iran classifies its airspace (AIP ENR 2.1)

Each aerodrome's CTR and ATZ is described in its AD 2.17 entry with its vertical limits, class and ATS unit; the controlling sector and its frequencies en route are published in ENR 2.1. Always check the AIP edition in force and current NOTAM — limits and frequencies change with AIRAC amendments.

• Airways, TMAs, CTAs and CTRs above FL200: class A.
• Airways, CTAs and CTRs at FL200 and below: class D.
• TMAs at FL200 and below: class C.
• Airspace outside airways, TMAs, CTRs and CTAs: class G.
• Between FL290 and FL410 inclusive the Tehran FIR is RVSM airspace.

Example — a VFR flight from Kish

A VFR departure from Kish starts inside the Kish CTR (class D, surface to FL105): a clearance from Kish Tower is required and VFR traffic receives traffic information on other flights. Leaving the CTR below the airways, the aircraft is in class G, where only flight information service is available on request. Climbing into an airway or CTA at or below FL200 means class D again — with a clearance and two-way radio contact with Tehran Radar on the sector frequency.