In between the Aerodrome Tower (TWR) (Link) and the Area Control Center (ACC) (Link), lies the Approach Control. This service is responsible for a big area over one or more airports. This airspace is a portion of a larger one, which is named Terminal Area (TMA). The TMA usually begins a few hundred feet over mean sea level and extends vertically until a height that varies depending on the traffic and the importance of the included airports. For instance, Athens TMA (including Hellinikon, Megara, Elefsis and Marathon airports) extends up to 46,000 feet, while Kos TMA (including only "Ippocrates" International airport) extends only up to 14,500 feet.

TMAs receive constant converging traffic that destines the included airports. Controlling such traffic is particularly difficult because airplanes are moving in a relatively limited area and all have the same destination. Additionally, there is departing traffic which has to be separated from the inbounds plus any terrain obstacles.

In case of simultaneous arrivals, pre-designated elliptic patterns have been published, which are called Holding patterns. These are located over the navigational aids (VOR-DME-VORTAC) of the TMA. The rule is to give priority to the airplane that arrives first over the nav-aid and is at lower altitude than the others. For the second plane that arrives over the spot, but not far enough behind the first one, delay is issued and it receives instructions to enter the Holding Pattern until a predefined time. If a third one arrives it is instructed to hold at a different altitude (higher) than the preceding.
In this way a "stack" of airplanes, which are flying in elliptic orbits, is formed until time comes for them to initiate approach. Delays, due to holding in the air, vary from 4 to 30 minutes. This is the main reason why it is necessary for all aircraft to be supplied with supplementary fuel. Nevertheless if a pilot declares insufficiency of fuel, his flight automatically receives priority clearance and is instructed to the nearest airport.

The specific nature of Approach Control and the immense increase in air traffic made the use of Radar indispensable. The "stacks" of airplanes, which were flying waiting for their time to come increased dangerously and the last airplanes had to orbit at altitudes as high as 28,000 feet, waiting there for 45 minutes! It was made clear, as early in the mid 60s that Athens TMA should be equipped with Radar as soon as possible. Procedural Control, although safe and familiar to all parties, became insufficient.

Athens Approach Control used Radar before all other Air Traffic Control services in Greece, improving delays in the air by a significant factor and cutting down all the approaches to the minimum distance needed. The Radar controller intervenes directly in the airplane's navigation giving detailed instructions regarding heading, altitude and speed thus separating it from other aircraft and terrain. Aircraft is now directed to follow the preceding even if it is at the same altitude as long as a minimum horizontal separation of 5 nautical miles exists! It is understandable now that the time and energy consuming Holding Pattern procedure is driven to obsoleteness, although it is not entirely excluded in extreme situations.

Since early 1999 Radar systems were installed at all the major Greek TMAs (Thessaloniki, Iraklion, Rhodes and Kerkyra). Air Traffic controllers currently use them on an advisory basis and it is estimated that they will be fully operational soon after personnel training is completed plus final adjustments and completion of all formalities.

The "Eleftherios Venizelos" international Athens airport is in its final trial phase and is expected to bring great changes to the Athens TMA due to the increased traffic anticipated and for the first time (in Greece) introduced parallel runway system. All the Standard Arrival and Departure procedures are undergoing major planning changes.

After all the above it is clear that Greek Air Traffic Controllers are going through a very interesting and demanding phase of their professional life that requires constant training in addition to the every day workload.

Athens, October 2000

Kostas Patouras
Athina/Makedonia ACC

http://fly.to/kpatouras.gr