The 30th annual conference decided to keep this item on the SC 1 Work Programme. During the committee B discussion on this work study item, SC 1 was asked to consider the methods to assess ATC sector capacity and the ability of ATFM organisation in Europe to match this capacity. At the 30th annual conference the ICAO observer presented two papers on ATFM; one on “Techniques for ATC sector/position capacity estimation” and one on “Application of automation in ATFM” (Flimsies 4 & 5).

In WP 54/B91 presented an overview of the developments in ATFM in Australia, Canada, Europe and the USA. New or further information from these regions or from other regions has not been received by SC 1.

As far as the capacity measurement methods are concerned, SC 1 considers that IFATCA does not have the scientific resources to challenge the two available studies, (DORA and MBB). IFATCA agrees the need for knowledge about the capacity of air traffic control sectors or ATC positions. First for long term planning purposes and second where shortage of capacity requires the application of flow control, it is necessary to know the available capacity in order to issue proper flow control measure. However, from the operational controllers point of view there are a number of critical remarks which can be made on these studies.

Before discussing these criticisms it may be useful to look at some and their explanation as given in ICAO EUR Doc. 003 ATFM (Prov. Edition):

a) Capacity – Ability of the ATC system, or any of its subsystems, or an operating position, to provide service to aircraft during normal activities. It is expressed in numbers of aircraft entering a specified portion of the airspace in a given period of time. The maximum peak capacity which may be achieved for a short period of time may be appreciably higher than the sustainable value.

b) Load threshold – A value, expressed in movements per hour, used in conjunction with air traffic counts to generate warnings. This value should represent the level of plannable traffic, i.e. traffic which could be expected to be known the Central Data Bank (CDB), above which capacity problems are likely to be encountered in section 3 of above mentioned ICAO document the relationship between and load threshold values is worked out. Where capacity values have to be estimated, available equipment, procedures, and staff should be taken into account. Furthermore, States have to provide load threshold values (LTV’s) for ATC sectors, significant points, TMA’s or aerodromes within their area of responsibility. In preparing LTV’s States should take due account of a number of factors, one of which is the method to calculate capacity.

On the basis of the information provided by the ICAO observer to the 30th annual conference (Flimsy 4 titled: “Techniques for ATC sector/position capacity estimation”) it can be said that these studies are not taking into account a number of factors such as human performance, system performance, and weather conditions which can be very important for the total sector capacity. Beside that, it is recognised in reports describing the DORA method, that it is difficult to define acceptable workloads from the capacity assessment methods. To be able to do that more experience is needed. Next to that it is recognised in the ICAO flimsy 4 that the methods used produce figures for a given set of circumstances such as available equipment traffic patterns, and staff. When these circumstances change, the outcome of the capacity assessment method likewise will change. Therefore, the method cannot be used universally for a given set of circumstances. Still SC 1 feels that a common set of factors should be considered when mathematical methods are used to assess capacity. Especially when the resulting LTV’s are used to spread the traffic demand over different sectors of different centres. Also SC 1 feels that the emphasis of these studies is too much directed to the capacity of a radar controller. SC 1 would prefer a method which looks to the capacity of a sector team i.e. assistant, planning coordinator , and radar controller. Also, the available technical equipment of all working positions, procedures, as well as back up procedures, equipment, and airspace configuration, should be considered. In principle, SC 1 feels that capacity figures should be based on normal operating circumstances. However, unusual circumstances should not be disregarded therefore some kind of buffer should be considered to give controllers the possibility to deal with unusual events. This buffer is probably difficult to quantify but should not decrease the capacity by an unrealistic high
percentage.

(Note: SC 1 was informed that an enhanced DORA study has been completed which considers some of the above mentioned points. Unfortunately this information reached SC 1 just before the closing date of this working paper and could not be incorporated in this paper. If the results of the new DORA study are available to SC 1 before the conference then there will be an update on this study given during the committee B meeting.)

In Europe it regularly happens that the present ATFM organisation cannot achieve its main purpose e.g. match traffic demand to the available ATC capacity. Be it that sectors are still overloaded in spite of flow control measures or that traffic encounters heavy delays while controllers have only a few aircraft to handle. Another factor causing overload situations is the cheating of the system by operators (e.g. not adhering to the correct flow control procedures) as discussed last year in committee B. The above mentioned facts only emphasise the need for the current development of the European Central flow Management Unit (CFMU). While the development continues, IFATCA should continue to monitor these developments in order to identify possible shortcomings and where necessary suggest improvements. (This is done via questionnaires from EVP EUR and input to the informal flow control meetings).

In 1991 one of the steps to develop the CFMU in Europe was the provision of load threshold values (LTV’s) by the contracting States to the DBE. The DBE will use these load threshold values together with demand data to generate overload warnings to the Central Executive Unit (CEU). The CEU can thereafter advise the relevant ATC unit through their Flow Management Position (FMP) and discuss the possible ATFM measures to avoid overloads. If no or wrong LTV’s are provided then consequently the DBE will generate no or wrong overload warnings. Therefore it is vital that much attention is given in establishing these LTV’s. As there are no common methods available, often the capacity is determined by experience, as are the LTV’s.

In IFATCA WP No 91/054 describing ATFM developments world-wide, conclusion 3.1 stated that: “In the future Air Traffic Management system, ATC is the primary component. ATFM is an adjunct to ATC in order to assist ATC in attaining its objectives. Therefore, it is ATC which should supply important data such as capacity values, load thresholds, planned sector configuration etc. Since this data is vital information for an ATFM organisation, it should be determined by operational ATC staff.” Following this conclusion and taking into account the earlier mentioned fact that capacity and load threshold values are often based on controller’s experience. IFATCA should ask for direct operational controller’s involvement in determining capacity and load threshold values. Where mathematical methods are used to establish capacity figures and LTV’s and where realistic ATC simulators are available, the use of these simulators to evaluate the results of the mathematical methods could be considered.

To conclude

Sector capacity measurement methods are of great importance for an efficient ATM organisation and close co-operation between ATC and ATFM. When sector capacity is assessed to establish LTV’s operational controllers should be involved and their experience used. Sector capacity measurement methods should have a common set of factors to be considered when assessing sector capacity and determining LTV’s. When capacity is assessed all factors should be taken into account, not only the radar controllers capacity, but the whole structure of sector organisation, equipment, airspace structure, procedures, and last but not least, the ability of the controller to do the job. Load thresholds should be so established that there is a buffer so that controllers are not forced to operate at maximum capacity all the time and allow for unusual circumstances.

It is recommended that:

The knowledge of sector capacity and LTV’s is of great importance for an efficient ATM organisation and for a close co-operation between ATC and ATFM. Therefore it is recommended that LTV’s are established for all sectors. As it is ATC which should supply important data to ATFM like LTV’s, it is necessary that operational controllers are involved in determining LTV’s. It is necessary to consider a common set of factors when using a capacity measurement method therefore it is recommended that IFATCA is involved in establishing the common set of factors for use in capacity measurement methods.