Study Implementation of 8.33 kHz in Europe and Determine if any Problems Exist at the Europe-Africa Interface

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Study Implementation of 8.33 kHz in Europe and Determine if any Problems Exist at the Europe-Africa Interface

42ND ANNUAL CONFERENCE, Buenos Aires, Argentina, 17-21 March 2003

WP No. 91

Study Implementation of 8.33 kHz in Europe and Determine if any Problems Exist at the Europe-Africa Interface

Presented by SC1


1.1  The 8.33 channel spacing, implemented by seven European States in 1999, has been extended on the 30th of October 2002 to 22 additional States through the so- called HEX (horizontal expansion) Programme. Europe disposes now of a very large block of 8.33 airspace with nearly 99 % of the aircraft fleet converted to this new technology.

1.2  Despite the fact that this very positive development has improved the safety of the central European 8.33 zone, as only very few safety concerns remain to be monitored, the extension of the 8.33 zone towards the outer borders of the initial 8.33 zone is very likely to bring to the surface new worries and safety problems requiring immediate attention.

1.3  The correct «8.33 filtering » of aircraft leaving the African continent northbound, approaching the European 8.33 zone has been identified as a potential safety hazard. The Northern African States using often less performant and sophisticated ATC- systems and sometimes even fighting to get adequate communication channels or having correct and updated FPL-data available might have difficulties to protect the southern European 8.33 sectors efficiently from dangerous penetrations by non- equipped aircraft.

1.4  Whereas the 8.33 programme was so far strictly restricted to European and ECAC- States, these new safety concerns might make it necessary to assess, study and mitigate them properly on a much wider scale.


2.1  The implementation of radios with 8.33 channel spacing in Europe, back in 1999 was certainly a great challenge. New procedures, including protection measures for the first sectors using this new and disparate technology had to be found and implemented. Safety hazard analysis and safety studies were required in order to identify and mitigate the known shortcomings and dangers of mixed radio operations (8.33 and 25 kHz).

2.2  By now, all this is of less actuality as it has been proven to all users, including pilots and air traffic controllers, that the 8.33 technology is at least as good as the « old 25 kHz ». Also, the mitigation procedures put in place, including the use of 8.33 phraseology and other 8.33 specific procedures, coupled with the very high number of airframes equipped with 8.33 have shown that 8.33 operations are generally very safe.

2.3  The spreading of 8.33 to the periphery of the European continent, particularly towards the south, using a technology that is used in one distinct area only is very likely to have created some new risks and safety concerns that need to be addressed and solved.

2.4  One of the most important measures to guarantee the safety of sectors and units using 8.33 is the protection offered by the Integrated Flight Plan System (IFPS), the central flight planning and flow control system of Europe. This system rejects systematically all flight plans of non-equipped aircraft requesting a cruising level of FL 245 or above (departing from inside the Integrated Flight Plan Zone (IFPZ)) in direction of any area where 8.33 is in use. This FPL-rejection is not possible for flights departing from outside the IFPZ. In Europe, all operators and aircrews have to pass via the IPFS to file a FPL, guaranteeing a high degree of protection. All European ATC units that are directly linked to IFPS will receive a warning message from IFPS if a FPL does not indicate 8.33 carriage. African units and sectors tasked to perform the filtering of 8.33 aircraft (to descend non-equipped aircraft) will not receive such a warning message. The African transition units therefore rely heavily on an efficient and correct filing of FPLs by the aircraft operators. Furthermore, it must be ascertained that the correct and updated FPL-messages are received by the units in order to have the actualised information available at the control positions. This is a very difficult task, taking into account the problems Africa has with the handling of time-critical flight plan data and updated ATC messages.

2.5  IFATCA has always insisted on the fact that nearly all, if possible all, issues linked to 8.33 carriage shall be solved on ground and via FPL handling. It was understood that the controller workload and the R/T load for operational controllers working these interfaces must be kept to the absolute minimum. Whereas this was quite well succeeded in Europe, mainly as a very performant tool called IFPS was available, concerns are now surfacing for Northern African and other outer-European units situated immediately adjacent to European 8.33 units.

2.6  The idea of the 8.33 programme was that the last unit, or the centre upstream, before entering an active 8.33 sector is responsible, in co-operation with the receiving first 8.33 sector, to « filter » aircraft accordingly. Normally this is also foreseen in the LoA (letter of agreement) concluded between the centres laying down the procedures to be used and applicable. This is of particular interest if a last minute diversion (aircraft is detected at handover to be not equipped) becomes necessary.

2.7  Such avoiding measures can be very difficult and time consuming, especially in high- density airspace or with poor radar coverage or when facing communication problems. They require extensive co-ordinations and tactical ATC-actions to bring the aircraft safely down to FL 245 or below before handed over below the active 8.33 sectors.

2.8  The interface problems at the southern European 8.33 border may require a much greater and more proactive involvement and co-ordination between EUROCONTROL (as program manager on behalf of ICAO) and the Northern African States that are concerned by 8.33 filtering.

2.9  As the extension of 8.33 states has occurred only 2 months before the closing of this working paper the time frame was too short to gather all the required information required to lay out in detail the problems encountered so far by the Northern African States in relation to the spreading of 8.33. Furthermore, several new 8.33 States (through HEX) have not yet converted their upper sectors to 8.33 technology so that the problems have not surfaced yet. Therefore it is very likely that the problems are rather slow to develop and reach the surface. But monitoring of the situation is certainly required.

2.10 Egypt is protected by several states and therefore is not directly involved in the active filtering of 8.33 aircraft. Libya is fully protected by Malta that is responsible to filter 8.33 aircraft towards Italy, as the first active 8.33 sector is with Rome ACC (northbound). The Malta MA has complained that roughly about 20% to 25% of the aircraft from Africa, northbound, are flying in without FPL data, what complicates the detection of 8.33 equipage considerably.


3.1  Almost all Northern African countries we have approached indicated either problems, or at least worries, about the handling and filtering of 8.33 aircraft for the Southern European 8.33 sectors situated either in Italy, France, Spain or Portugal, despite the fact that not all States have gone for 8.33 so far.

3.2  As the extension and change towards 8.33 of most Southern European countries occurred only two months ago (except France), and also due to the fact that many of the countries were rather late, or even haven’t converted their sectors to 8.33 yet, the problems haven’t surfaced yet as anticipated and expected.

3.3  Nevertheless, there is a certain degree of uncertainty and confusion about the tasks and workload expected by adjacent 8.33 sectors. Also the lack of training in the Northern African states is certainly a problem.

3.4.  It is expected when this change happens that the problems will surface on a widespread basis and IFATCA will be able to gather much more concise and representative data of the problems encountered. So far we are rather guessing than knowing for sure, also strong indications are there for a problem.

3.5.  Therefore, it is safe to say that the interface problems at the southern European 8.33 border will require a much greater and more proactive involvement and co-ordination between EUROCONTROL (as program manager on behalf of ICAO) and the Northern African States involved.

3.6.  Issues such as controller training, exchange of data, conclusion of workable LoAs are certainly a problem that needs to be addressed and solved between the different players and stakeholders.

3.7.  It is proposed to put the subject to the SC 1 work schedule for the 2004 world Conference in order to get more details and material in order to propose policy, if deemed necessary.


It is recommended that:

4.1  This paper be accepted as information material.

4.2  This subject be put on the work programme of SC 1.

Last Update: September 29, 2020  

March 22, 2020   474   Jean-Francois Lepage    2003    

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