8.33 kHz Horizontal Expansion

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8.33 kHz Horizontal Expansion

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

WP No. 104

8.33 kHz Horizontal Expansion

Presented by Akos van der Plaat


1.1  In addition to the 7 Initial States, 22 States have removed exemptions related to 8.33 kHz channel-spacing on 31 October 2002.

1.2  This report will give an update on the EUROCONTROL 8.33 kHz Horizontal Expansion Programme (HEP), and all related programmes and projects, since the annual conference in Cancun.

Horizontal Expansion Programme

2.1 The preparation of all involved HEP States has been closely monitored by EUROCONTROL. The rate of equipage has been monitored closely as well, by using several databases combined with information provided by aircraft operators in and surrounding the area. This, combined with a graduate introduction of 8.33 kHz channel spacing and lessons learnt from the initial States has lead to the following statement by the 8.33 HEP Programme manager: “All necessary pre-requisites should be in place to allow removal of exemptions on 31/10/2002”.

2.2 Although the rate of equipage has been titled as extremely high (over 98%), it remains crucial to keep monitoring the handling of State aircraft (a State aircraft is defined as: “An infrequent user, not exceeding 30 hours per airframe per year”). An average of 35 State aircraft operate daily in the IFPS zone above FL245, demanding for correct handling procedures to be in place. IFATCA has put emphasis at several occasions on these procedures, to prevent that controllers are exposed to an extreme increase of workload. Besides this, concerns have also been expressed by IFATCA on the fact that a number of States have no, or just limited, UHF coverage.

2.3  The number of frequency conversions have been disappointing to the Programme Support Office (PSO), since the aim of the project has been “to maximise the number of conversions, in order to provide VHF spectrum capacity and planning flexibility”. With the HEP, the number of conversions achieved by the 7 initial States have not been exceeded by the 22 HEX States. Several States have removed exemptions without converting to 8.33 kHz channel spacing at the implementation date. Examples are Ireland (under review for 2005), Romania (2003), Spain, (2003), Sweden (between 2003 and 2005) and Poland (no conversions planned and reviewing Climax situation).

2.4  The graduate introduction of 8.33 kHz Channel spacing will most probably have a positive impact on safety, since it will create more time for several States adjacing to the Horizontal Expansion area. The Safety Regulation Committee (SRC) has stated that: “the 8.33 kHz Horizontal Expansion Programme will be its main EATMP priority in 2002”. This has lead to several safety studies done in the past, but also to one more safety study expected. The 8.33 kHz Safety Policy, the 8.33 kHz Validation Study and the National Safety Plans have been delivered at an earlier stage, while the last study has been the Pre-Implementation Safety Case. This study has considered the launch procedure, the gradual introduction of 8.33 channels, IFPS functionality, State preparation and readiness of operators and their rate of equipage. The Post-Implementation Safety Case is expected in 2003.

2.5  IFATCA has send out two questionnaires, the first is included as Annex A, and the second as Annex B. The first questionnaire has been used to check if all necessary awareness training and system requirements have been in place before 31 October 2002. The second questionnaire has been send out to monitor the post- implementation period and report all irregularities to the EUROCONTROL 8.33 PSO. The feedback received from the European Member Associates on both questionnaires has been very disappointing, not enabling the 8.33 Representatives to use the outcome of the questionnaire and to give feedback to the PSO.

2.6  No major incidents were reported in the period after 31 October 2002. The initial indications after implementation were that safety levels have been maintained, and that there has been a minimal impact on operations.

Vertical Expansion Programme

3.1  At the 44th meeting of the ICAO EANPG, it was decided to proceed with 8.33 kHz vertical expansion. A short outline of this meeting below:

“Conclusion 44/38 indicates the need to minimise the impact on GA VFR and State aircraft. The following phases are identified, on the understanding that individual States have the right to grant exemptions for aircraft and/or airspace volumes:

  • Phase 1: above FL-195 in the ICAO EUR Region from 2006;
  • Phase 2: as required in particular terminal control areas (TMA)s and control zones (CTR)s where individual States have determined this to be a practical measure for alleviating VHF congestion; and
  • Phase 3: in designated controlled airspace in the ICAO EUR Region from 2009 onwards.”

With the 3 phases described above, one scenario that had been identified at an earlier stage will not be implemented. This fourth scenario was considering VEX in all airspace.

The Vertical Expansion Study (VES) is one that mainly addresses the technical impact, while the operational impact has only been partially addressed. IFATCA has not opposed to the principle of VEX, but a number of critical remarks have been made on the VES. The remarks have been noted and some changes have lead to the conclusion above.

3.2  Further developments on Vertical Expansion (VEX) should be closely monitored by IFATCA, preferably by a new representative.


4.1 At the annual conference in Cancun, rather firm policy was accepted in response to the proposal for amendment of ICAO Doc 7030, European Regional Supplementary Procedures. The policy mainly focused on not changing phraseology without an independent safety review, but also retaining the word decimal in transmissions of channels.

4.2  A meeting was organised at ICAO EUR Office in Paris to discuss the proposal for amendment of Doc 7030. In the discussion that took place, IFATCA mainly opposed to changing the phraseology without a proper impact assessment. After long discussion, a new proposal was drawn up, included as Annex C.

4.3  A simulation has been organised between 24 and 27 September 2002 at the ANS Training Centre in Riga (Latvia) to assess the impact of the new phraseology on controller workload. The primary objectives of the simulation were:

a) To assess the impact on controller workload, in both enroute and approach control operational environments, stemming from the use of all six digits of the numerical designators for all VHF air-ground communication channels;

b) To assess the impact of the specific proposal to not pronounce the term “Channel”, in conjunction with the numerical designators of VHF communication channels which are based on a channel spacing of 8.33 kHz; and

c) To assess the requirement for transition procedures, intended to ensure that aircraft which are not equipped with 8.33 kHz channel spacing radio equipment, are excluded from airspace where the carriage and operation of such equipment is mandatory.

At this simulation, three RTF conventions were defined:

  1. In line with the proposal to the Co-ordination Group (COG) meeting of May 2002, specifically, the pronunciation of all six digits of the numerical designators for all channels and no pronunciation of the term “Channel” for 8.33 channels;
  2. All six digits of the numerical designators of all channels are used, except for the case of certain channels which contain multiple trailing zeros. No pronunciation of the term “Channel” for 8.33 channels was required in this convention; and
  3. The current published method for the communication of VHF communication channels.

The simulation was solely based on subjective workload, all the participating controllers were asked to give feedback in the form of written answers and comments to written questionnaires, which were developed with specific regard to a given simulation day’s activities. The airspace simulated covered both enroute and terminal airspace and both 8.33 and non-8.33 airspace.

The conclusions of the simulation were not surprising. The largest decrease in workload was measured with RTF convention 2, although this convention had not been identified as a possible solution. This because of the fact that the pilot can expect anything between four and six digits, and confusion is very likely. RTF convention 1 was second, with a large difference in subjective workload with RTF convention 3. In an environment where all six digits were pronounced, the simulation concluded that the term “channel” would provide no added value and could be withdrawn. In comparison to the existing method of pronouncing numeral designator for channels, the simulation concluded that not pronouncing the term “channel” in combination with the pronunciation of all six digits, represented a general decrease in controller workload. As a solution for the transition procedures, ATS automated display systems should be available to the controller, preferably within the radar label.

4.4 The outcome of the simulation and a way forward was discussed at a second meeting. All parties agreed on the fact that RTF convention 2, although proven to be the most preferable convention, would not be further developed. IFATCA opposed to the fact that the simulation objectives did not address the expected problems, but also to the limitations of the simulation organisation. The simulation has proven that the proposal agreed at the first meeting would lead to a reduction in controller workload, and a way forward on that proposal was discussed. It was stated that in the implementation process, EUROCONTROL would conduct a safety assessment. The aimed introduction date was set at 30 October 2003.

4.5  At the 44th meeting of ICAO’s European Air Navigation Planning Group (EANPG), IFALPA opposed to the agreed proposal. Since IFALPA had not been able to attend any of the meetings where the subject was discussed, it had not been possible to reach consensus on the way forward. A third meeting will be organised with all parties concerned and the proposal for amendment will be processed in accordance with the agreed ICAO procedures.

4.6  If the third meeting will lead to a proposal not in line with IFATCA policy, SC1 should be tasked to review 8.33 kHz phraseology on next years work programme. A full update on the matter will be given at the annual conference in Buenos Aires.


5.1  Continuing work is needed by IFATCA within the various 8.33 kHz channel spacing programmes. The HEP will be closed in 2003 and my responsibility for that specific programme will cease to exist by the closing date. I will continue work on the 8.33 kHz phraseology proposal, a task that will probably end in 2003 as well. There is a need for IFATCA to seek for a new representative for the Vertical Expansion Programme (VEP), since I will not continue my tasks on that terrain. The VEP is at an early stage and it would be very beneficial to step into the programme as early as possible.

5.2  I would like to express my gratitude to Christoph Gilgen, who has been the only 8.33 representative in the initial phase and at the beginning of the HEP, it has been a pleasure to work with him. I would also like to thank the Dutch Guild, who supported me and enabled me to attend all of the meetings.

Appendix A – First Questionnaire



  1. Training : did you have particular training courses to prepare the implementation of 8.33?
  2. Were you trained and instructed to use the correct 8.33 phraseology?
  3. Were you trained how to handle exempted State flight using UHF?
  4. Are you aware about the status of your neighbouring centres related to UHF coverage?  Do you know if all the adjacent centres going for 8.33 have an UHF-frequency and can accept exempted flights or at least do you know what procedure do you have to use for those flights?
  5. Will the operational manuals of your unit be adapted and updated to include 8.33 and its procedures?
  6. Do you have a change of LOA (Letter of agreement) for October 31, 2002 with all neighbouring centres to introduce the procedures for handling 8.33 aircraft?
  7. If you have seen this DRAFT LOA, is the handling of State aircraft included?
  8. For those States at the 8.33 periphery : in the DRAFT LOA is the handling of last minute diversions set down (note: last minute diversions means that when the adjacent centre wants to change an aircraft to you it is discovered that it is not 8.33 equipped and must be descended immediately)
  9. Related to showing the equipment (e.g. 8.33 or not 8.33) on your flight progress strips after October 31, 2002. Will this be made or not?
  10. If it is made (equipment on the progress strip) how is it made? Manually by assistants or OPS-personnel, directly and automatically from IFPS/CFMU, from the flight plan either manually or automatic, OLDI exchange from adjacent centre? Any other method?
  11. Do you have a special warning message or sign to alert you of a not-equipped aircraft (e.g. different color of something like that)?
  12. Will you have the M (for military) and the STS/833EXEM/STATE on your flight progress strip? This is important for handling exempted flights.
  13. Will you have the STS/UNKNOWN on your flight progress strip ?

Appendix B – Second Questionnaire




  1. How many sectors within your unit (full configuration, all sectors opened) use frequencies with 8.33 kHz channel spacing?
  2. How many sectors using 8.33 kHz channel spacing (full configuration, all sectors opened) are bordering your airspace?


  3. Do you have UHF frequencies available for the handling of non 8.33 equipped state aircraft?
  4. Do you have VHF (spare) frequencies available, as no UHF is available? Or, alternatively, low level frequencies with 25 kHz spacing?
  5. How many UHF frequencies do you have available in total for all 8.33 sectors?
  6. How many VHF (spare) frequencies do you have available in total for all 8.33 sectors?
  7. Do you use the (spare) VHF frequencies only for the handling of 8.33 exempted state aircraft, or do you use them for other operations as well?
  8. Is it possible to couple the UHF/VHF frequencies to the 8.33 frequency used for regular traffic (so-called partyline, resulting in the pilots being able to hear other transmissions)?
  9. Do you think that the number of frequencies (UHF and/or VHF) available to handle 8.33 exempted flights is sufficient? Please answer this question by taking into account the number of aircraft to handle and the number of sectors that must share these frequencies.


  10. How do you co-ordinate with adjacent sectors within your unit, if you have to share UHF or VHF frequencies? (e.g. in Switzerland it happens that several aircraft are handled in different sectors at the same time and different controllers speak on the same UHF frequency)
  11. How do you co-ordinate with the adjacent sectors/units when you transfer a non-equipped aircraft? Do you co-ordinate manually (by telephone) or do you have silent transfer of control procedures (in combination with some sort of automatic exchange) laid down? If yes, please explain.


  12. Have you observed a lot of exempted state flights that fly on a very frequent basis in your airspace with the same airframes? (exempted state flights are expected to be infrequent users, not exceeding 30 flight hours per year) If so, did you take any action?
  13. What is the procedure if an aircraft is discovered just prior hand-over the next sector, as non-equipped flying within 8.33 airspace? Can it continue en-route and you co-ordinate with next sector, or will you have to instruct the pilot to hold and then co-ordinate for a solution?
  14. Did you have any requests of civil non-equipped aircraft to fly within 8.33 airspace, for a check- or test flight? How are these flights handled?
  15. Did you have any requests of civil non-equipped aircraft to fly within 8.33 airspace, for operational reasons (e.g. turbulence or other weather related reasons)? How are these flights handled?


  16. Do you receive an immediate automatic update of the change in status of a flight? This can be either on the (electronic) strip or in the label.
  17. Who enters this update in your system? This can be manually by assistant/controllers, or also automatically by the system using OLDI/IFPS/FPL information.
  18. How are updates of aircraft equipage entered in the system in the pre-activation phase? (e.g. the aircraft type of a repetitive flightplan changes) Once again manually or automatically.
  19. Do you exchange 8.33 equipage and status with adjacent units by using OLDI? If not, how is this exchange of information arranged?


  20. Do you have any problems or incidents that have not been addressed by the questions above? You can also use this opportunity to give us other feedback on 8.33 related subjects.

Appendix C – Proposal for amendment of the regional supplementary procedures EUR Region (DOC 7030/4)

(Serial No.: EUR/NAT-S 01/35-EUR RAC/13)

a) Regional Supplementary Procedures:

Doc 7030/4 EUR, Part 1, Rules of the Air, Air Traffic Services and Search and Rescue, as modified by Amendment 201 dated 31 October 2001.

b) Proposed by:

The European Air Navigation Planning Group (EANPG).

c) Proposed amendment:

Amend Part 1, Section 4, Air-Ground Communications and In-Flight Reporting, as follows:

“4.2 Phraseology related to 8.33 kHz channel spacing (P-ATM, Chapter 12)

4.2.1 Aircraft operating or intending to operate in airspace where 8.33 kHz channel spacing has been implemented shall use the phraseology as shown in Table 1.

Table 1. Phraseology related to
8.33 kHz channel spacing

Circumstances Phraseology
To request the 8.33 capability of the radio equipment CONFIRM EIGHT POINT THREE THREE
To indicate 8.33 kHz capability *AFFIRM EIGHT POINT THREE THREE (2)
To indicate lack of 8.33 kHz capability *NEGATIVE EIGHT POINT THREE THREE
To request UHF capability CONFIRM UHF
To indicate UHF capability *AFFIRM UHF
To indicate lack of UHF capability *NEGATIVE UHF
To request the status in respect of the 8.33 exemption CONFIRM EIGHT POINT THREE THREE EXEMPTED
To indicate 8.33 kHz exempted status *AFFIRM EXEMPTED
To indicate 8.33 kHz non exempted status *NEGATIVE EXEMPTED
To indicate that a certain clearance is given because
otherwise a non-equipped or non-exempted aircraft
would enter the airspace of mandatory carriage


(Note 2: * Denotes pilot transmission)

4.3 Assignment of VHF communications channel (A-10, Vol. II –

4.3.1 For identification of VHF communication channels, all six digits of the numerical designator shall be used to identify the transmitting channel in radiotelephony communications.”

Renumber subsequent paragraphs.

d)  Proposer’s reason for amendment:

The carriage and operation of 8.33 kHz channel spacing capable radio communications equipment became mandatory in the ICAO EUR Region on 7 October 1999 for flights above FL245. To accommodate this change, the European Regional Supplementary Procedures (SUPPS) (Doc 7030) had been amended, including the procedures related to radiotelephony.

During and after its implementation, operational personnel, air traffic controllers and pilots raised concerns about some confusion that had stemmed from the use of the phraseology applicable in airspace where 8.33 kHz channel spacing radios were being used. The following illustrates some of the areas where confusion has arisen:

a)  difference between “frequency” and “channel” values;

b)  confusion in when to pronounce four, five or six digits;

c)  confusion in when to add “5” or when to add “0” (e.g. many pilots select 130.055 when instructed to change to 130.05, (should have selected 130.050), and

d)  two different types of phraseology in the same airspace.

This amendment proposal will eliminate the current confusion and pave the way for a global procedure dealing with the assignment of channels, irrespective of the channel spacing being used.

e)  Proposed implementation date of the amendment:

As soon as practicable after approval by the Council.

Proposal circulated to the following States and international organizations:

Albania Indonesia Slovakia
Algeria Ireland Slovenia
Argentina Israel South Africa
Australia Italy Spain
Austria Japan Sweden
Azerbaijan Kazakhstan Switzerland
Belarus Kyrgyzstan Tajikistan
Belgium Latvia The former Yugoslav Republic
of Macedonia
Brazil Lebanon Tunisia
Bulgaria Libyan Republic Jamahiriya Turkey
Canada Lithuania Turkmenistan
China Luxembourg Ukraine
Croatia Malta United Kingdom
Cuba Morocco United States
Cyprus Netherlands Uzbekistan
Czech Republic New Zealand Venezuela
Denmark Norway Yugoslavia
Egypt Poland
Estonia Portugal Eurocontrol
Finland Republic of Moldova IACA
France Romania IAOPA
Georgia Russian Federation IATA
Germany Saudi Arabia IFALPA
Greece Senegal IFATCA
Hungary Singapore IBAC


f) Secretariat comments:

This amendment proposal would bring the current procedures used in the EUR Region into line with ICAO provisions and especially those of Annex 10.

– END –

Last Update: September 29, 2020  

March 21, 2020   776   Jean-Francois Lepage    2003    

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