Compliance with Air Traffic Flow Management Measures

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Compliance with Air Traffic Flow Management Measures

30TH ANNUAL CONFERENCE, Port of Spain, Trinidad & Tobago, 22-26 April 1991

WP No. 59

Compliance with Air Traffic Flow Management Measures


Air Traffic Flow management (ATFM) measures are required when the capacity of the ATC system is insufficient to meet the demand placed upon it by aircraft operators wishing to fly through the system, or a particular part of it. In those parts of the world where ATFM is required different arrangements have been made to cope with varying degrees of success.

In Europe, particularly throughout the summer months, a multitude of restrictions are required by many ATC Units. Some are caused by shortage of ATC staff at airports/ATCC’s, or by inadequate equipment or procedures; some are required because there are insufficient aircraft parking spaces at a particular destination airfield, and to have more aircraft arriving than can be accommodated on the apron is certainly not helpful to ATC. In other words , flow measures are implemented to protect ATC from “overload” situations.

The mechanics of reducing the number of aircraft that can be handled safely also varies. Some countries issue times at which en-route points must be crossed; other countries calculate departure times to ensure compliance with other countries’ requirements. It is usual for the operator or pilot to be required to obtain the slot; it is not unusual for ATC, either at the departure airfield or in the en-route centres, to be totally unaware of the individual slot so obtained.

At its best, strategic flow management planning ( based on a wide variety of data sources) is supplemented by tactical adjustments on a daily basis . given the right equipment, procedures and legislative backing this can lead to an ordered stream of aircraft entering the airspace subject to restriction. This is to everyone’s benefit. Controllers are not subject to dangerous overload situations and pilots are not required to spend lengthy – and costly – time in en-route or terminal area holding patterns, where their presence only adds to the ‘difficulty factor’ and creates a further reason for flow measures. Where delays are considered necessary to maintain a safe situation, time is spent on the ground.

In the last few years, a multitude of flow measures have been necessary to overcome the problems listed in para. 1.2 above. During that time – and as the restrictions have resulted in greater delays – it has become apparent that a growing number of operators and pilots are choosing to ignore these ‘slot’ times. The result is that a significant number of extra flights arrive over a particular point outside their allocated slot time and dangerous situations occur. Action has been taken on many occasions to try to resolve the problems, including direct contact with the operators and ATC at the departure airfield. In general the results are frustrating and ineffective. The pilots concerned see no reason to comply with slots that are not monitored, and are often encouraged to depart outside their slot time . many ATC units do not see flow management as any concern of theirs, particularly if the difficulties leading to flow measures are not present in their airspace.

The UK Guild believes that this situation is no longer acceptable, particularly in the high density traffic areas of Europe. There is clearly a need for effective flow management and for this to work there must be compliance with flow management measures. As this is demonstrably not possible with a voluntary system, the Guild believes that it is necessary for an effective monitoring system to be established. Such a system already exists in the UK whereby, aircraft are issued with ‘approved departure times’. It is the responsibility of ATC at the airfield of departure to ensure that the departure time is compiled with . The system works. It applies to all airfields in the UK which include some of the busiest in Europe. Ensuring that an aircraft does not depart before its slot time is , the UK believes, the only effective way to guarantee compliance.

It is also proposed that, in time, slots be made widely available to en-route controllers (e.g. time over sector entry points on data displays). This is not to say that en-route controllers should be required to ensure compliance with such times, but it follows requests by UK en-route controllers who believe that they should be more involved in the overall ATC picture affecting them. If a controller is under pressure then clearly he/she will not be in a position to use such information, but there will be many occasions when such information will, for example, alert the controller to a flow management plan that is clearly going wrong, or suggest to him that re-routeing a particular aircraft (or group of aircraft) may adversely affect a sector further down the line. Action by controllers on a quiet sector may prevent an overload on a busy sector. As members of an international federation we cannot afford to have an attitude which looks only at problems or solutions in a local way. Aviation, more than most other industries, needs international solutions to problems.

To Conclude

The capacity problems in the high density traffic areas of Europe are such that the current system of voluntary compliance with flow management measures applied in many States is potentially dangerous. Urgent action is necessary to ensure that flow measures – imposed to ensure safe levels of traffic are not exceeded – are complied with. It would be beneficial to the overall scheme of traffic management, in an international context, if en-route controllers were to be made aware of flow measures applied to aircraft under their control, affecting them of their colleagues.

It is recommended that:

It is recommended that IFATCA recognises the potentially dangerous situations that can arise when slot times are not adhered to That in the European Region , ATFM utilise ‘ departure time slots’ as a means of regulating air traffic and that where a departure slot time is issued that it be passed to the departure airfield. That it is the responsibility of the aircraft operator to be ready for departure to meet the assigned ATFM departure slot. That civil aviation administrations pursue with the utmost vigour those operators who consistently fail to comply with ATFM measures.

Last Update: September 20, 2020  

December 2, 2019   283   Jean-Francois Lepage    1991    

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