CNS/ATM
A Look At What It All Means. 

Air Traffic Controllers have been hearing about FANS (Future Air Navigation Systems) and more recently the CNS/ATM Concept. This article introduces the ICAO CNS/ATM Concept to Trinidad and Tobago Air Traffic Controllers and attempts to explain in hopefully simple language the meaning of the terms and how ATCOs will be affected by the changes.

Firstly, CNS/ATM represents the ICAO conceptualisation of the various components of the Air Navigation Services viz. C-Communications; S- Surveillance; ATM- Air Traffic Management.
This topic will be addressed with a look at the individual components, identifying what exists now and what is to come.

COMMUNICATIONS

Today, when we consider this item we think in terms of VHF (Very High Frequency) for communications with aircraft that are in range and a signal which goes directly from ground to aircraft and vice versa (more commonly known as line- of- sight communications); and in terms of HF (High Frequency) for communication with aircraft that are operating in areas very far away from land masses (or more specifically antennas). Air Traffic Controllers are aware of the limitations of both these systems of communications: VHF with its line-of-sight requirement is prone to all types of interruptions or breaks in communication; HF on the other hand is subject to propagation limitations including sunspot activity, atmospheric interference, etc.

In the future, air-ground communications will be Satellite-based for both voice and data. In the initial stages, HF maybe maintained for communications over the ocean until such time as satellite communications are available. The tremendous advantages of satellite-based communications cannot be underscored.

NAVIGATION

Today, VORs (Very High Frequency Omni-Directional Radio Range) and NDBs (Non-Directional Beacons) satisfy the enroute requirement for overland flight; VORs, NDBs, ILS (Instrument Landing System) and MLS (Microwave Landing System) satisfy the Approach and Departure phases of flight; on - board navigation systems such as INS/IRS and long range navigation systems like VLF/Omega and LORAN C are required for long range flights.

In the future, Area navigation (RNAV) capability will be progressively be introduced with the ICAO Required Navigation Performance (RNP) Standards. Global navigation satellite systems (GNSS) will provide worldwide coverage for enroute navigation and for CAT I precision approaches. NDBS, VORs and VOR/DMEs (Distance Measuring Equipment) will be progressively withdrawn.

SURVEILLANCE

Today, Surveillance is limited to PSR (Primary Surveillance Radar)  and Secondary (SSR) Surveillance Radar in Terminal Areas and areas of high density traffic; Pilot Reports (PIREPS) on HF and VHF Voice (when in range) in the procedural environment.

In the future, PSR will be progressively phased out only being used in areas where absolutely required because of the nature of the service provided and for specific geographical characteristics. SSR Mode A/C and S will be used in Terminal Areas and high traffic density airspaces.

A system called Automatic Dependent Surveillance (ADS), which uses Satellite technology to download digital data of aircraft position to ATM Units and to upload ATM related instructions to the aircraft will be employed extensively over the far reaches and even in Terminal Areas. ADS may eventually become a supplement to SSR.

In Oceanic Areas, where position reporting on HF is the only means of surveillance, ADS will provide a significant early benefit and be the basis for potentially significant enhancements in flight safety. With ADS supported by direct pilot/ controller communications, ATS (Air Traffic Services) in a procedural airspace will be provided in much the same manner as in Radar Airspace. With ADS also, the improved and more accurate position reporting would redound to the reduction in Separation Minima as obtains in today's procedural environment. Such reductions will alleviate delays and diversions from preferred flight paths and result in reduced operating costs when compared to today's operations in such airspaces.

AIR TRAFFIC MANAGEMENT

Air Traffic Control, as we know it today, is accomplished through position reports interpretation in the purely procedural environment and through the interpretation of visually represented position information and using this data to determine the spacing between aircraft.

The inefficiencies of the present systems place considerable burdens on the airlines. This is not to say that the systems are unsafe; rather they can be considered to be not cost efficient enough for airlines operating in the extremely competitive environment of today. These inefficiencies include: the requirement to fly circuitous departure and arrival procedures; indirect fixed routes between destinations determined by the position of ground-based navigational aids; operation of aircraft at inefficient altitudes, speeds and in unfavourable winds; and insufficient flexibility to permit optimum management of weather related disruptions. These problems manifest themselves in increased flight time, direct increases in operating costs with the resultant reduction in productivity on the airline side.

Airlines stand to gain significantly in the future as improvements to the current Air Traffic Control and flow Management Systems merge and evolve into Air Traffic Management. Coupled with the gains expected on the CNS side, the increased capacity expected on the ATM side spells greater cost benefits for airlines. How would this impact on safety, with all this increased capacity? Well, it is expected that the parameters for conflict detection will also change significantly with greater use of computers at ATM units designed to take information directly from aircraft, process the position data, determine whether conflicts exist and provide options to the
ATCO.

Yes, CNS/ATM proposes significant challenges for User and Service Provider. We eagerly await it.

Malcolm DePeiza