Air Traffic Services

15.1The Air Traffic Services (ATS). Annex 11 to the Chicago Convention lays down the SARPs for the establishment of an Air Traffic Control services in each of the contracting states. Each state is required to establish an authoritative body responsible for setting up and regulating the operation of the ATS of the state. In the UK the body responsible is the UK CAA and the operating organization is National Air Traffic Services (NATS).

15.2Document 4444. Because the SARPs of Annex 11 are (by necessity) insufficiently detailed, PANS ATM (Air Traffic Management) (Document 4444) is published by ICAO as the definitive reference for the establishment and management of an ATS. PANS ATM is mainly directed to ATS personnel; however, flight crews should be familiar with the content of the sections relating to ATM; ATS and separation; ADS and CPDLC; ATIRs and RPL.

15.3Objectives. The objectives of an ATS are to:

•Prevent collisions between aircraft;

•Prevent collisions between aircraft on the manoeuvring area and obstructions thereon;

•Expedite and maintain an orderly flow of air traffic;

•Provide advice and information useful for the safe and efficient conduct of flights;

•Notify appropriate organizations regarding aircraft in need of SAR aid, and assist such organizations as required.

15.4ATS Divisions. ATS comprises three divisions:

•Air Traffic Control Service

•Flight Information Service

•Alerting Service

15.5ATC Service. The ATC Service is divided into three sub-divisions:

•Area Control Service. The provision of ATC for controlled flights within CTAs and en route in FIRs and UIRs.

•Approach Control Service. The provision of ATC for controlled flights associated with arrival and departure. Usually provided within CTRs.

•Aerodrome Control Service. The provision of ATC to aerodrome traffic at controlled aerodromes.

15.6 The Need for ATS. An ATS is set up in consideration of the following:

• The types of traffic involved

• The density of traffic

• The meteorological conditions

• Other relevant factors (e.g. mountainous terrain, extensive sea areas, limited navigational facilities etc...)

15.7 ACAS. The carriage of ACAS by aircraft in a given area will not be taken into consideration when determining the level of service required to be established.

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15.15Basic Responsibility. When flying in accordance with an ATC clearance, the pilot is not relieved of the basic responsibility for ensuring the safety of the aircraft, including terrain avoidance, and that of other air users. Likewise, the Rules of the Air apply to any flight proceeding in accordance with an ATC clearance. When an aircraft is under radar vectoring, the radar controller will issue clearances such that the required obstacle clearance will exist at all times.

15.16Application. The practical application of ATC clearances is to provide a method whereby ATC gives instructions to aircraft to facilitate separation. In general, within CAS, IFR flights are always separated from other IFR flights. In classes B and C, IFR is separated from VFR and in class B, VFR is separated from other VFR. Within a CTR it is normal practice to separate SVFR flights.

15.17Contents of a Clearance. Clearances are to contain positive and concise data and shall be phrased in a standard manner. An ATC clearance should include:

•The aircraft identification as shown on the FP;

•Any clearance limit;

•The route of the flight;

•Level allocated for the flight (or for the initial/current part of the flight);

•Any other necessary instructions or information, such as SIDs, STARs, communications or

clearance expiry time;

•Transition level in approach clearances if so prescribed or when requested by the pilot;

•QNH (except when it is known that the aircraft has already received the information): when first cleared to an altitude below the transition level; in approach clearances; in clearances to enter the traffic circuit; in taxi clearances for departing aircraft.

In order to expedite the delivery and reading back of clearances, standard phraseology may be used such as “cleared via flight planned route to ….” or “cleared via Midhurst departure 2G …..” or “cleared via Ockham 1D arrival”. In such cases the pilot will be required to refer to the reference document or procedure plate.

15.18 Clearance Co-ordination. The responsibility for issuing a route clearance for a flight rests with the ACC of the FIR in which the flight originates. Ideally, before issuing a clearance, an ATCU would co-ordinate (agree) a clearance with all the other ACCs en route. In practice this is not feasible especially for long intercontinental flights. In this case, the ACC would issue a clearance limited to the initial FIR or where the flight time in the originating FIR is short (e.g. flights originating from Heathrow entering the Paris FIR), it would be essential to coordinate with at least the next FIR to be entered. Where it has not been possible to co-ordinate the clearance for the entire route, the aeroplane would be given clearances on a rolling (downstream) basis from FIR to FIR. Under certain circumstance it may not be possible for the current ACC to obtain a downstream clearance from the subsequent FIR in which case, the aircraft may be requested to originate communications with the downstream FIR and obtain a clearance prior to entering the airspace of that FIR.

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