Alpha Numeric Callsigns

Alpha Numeric Callsigns

26TH ANNUAL CONFERENCE, Nairobi, Kenya, 27-30 April 1987

WP No. 33

Alpha Numeric Callsigns


In 1986 at the Cost Rica conference IFATCA’s policy regarding alpha numeric callsigns, agreed at the 1985 Athens conference, was deleted. Currently therefore IFATCA has no policy on this specific subject.

Prior to both these events, the Air Navigation Commission (ANC) of ICAO considered the proposal (developed mainly by IFALPA) for a specific alpha numeric format (anaa) preceded by the company designator, and abbreviated after the first RT call to designator + aa. Before agreeing to its adoption in Annex 10 Vol II the ANC requested the ICAO Secretariat to provide more information on the trials and simulations which this format had been subject to.

Based on the information provided by the Secretariat (some of which has been questioned with regard to its accuracy) the ANC was not convinced that the ‘IFALPA’ alpha numeric system was a viable proposition despite support for it by the EARC SG. The ANC then asked the Secretariat to set up an ad-hoc group to look at the problem all over again. None of the members of the EARC SG was included in this ad-hoc group. At the time of writing this paper , the proposals developed by the ad-hoc group have been circulated for comment and , in the main, rejected by IFATCA and IFALPA as unworkable.

The following questions were posed in Costa Rica :

  1. is there a problem ?
  2. what is the problem ?
  3. are we trying to solve a simple problem of poor RT discipline with very technical and complex solutions ?
  4. can some problems be solved with equipment ?

Is there a problem ?

In 1979 IFATCA SC 1 distributed a questionnaire to MA’s. The replies (20!) indicated that callsign ambiguity was a problem 7 years ago – it is unlikely to have got any better as the traffic levels have increased since then.

What is the problem ?

19 of the 20 MA’s indicated that confusion was caused primarily by the use of the airline flight-number type of callsign . However, it was not only flight numbers which became confused one with another. It was the actual number of numbers being spoken on the frequency – headings, frequencies, squawks, flight levels and of course flight numbers; in other words number saturation.

Airlines use figures within the flight number for particular purposes and many of them have the same basic logic. The first flight of the day, for example, usually ends in ‘1’, the return flight being ‘2’ , the next outbound ‘3’ and so on. Therefore in the morning it is likely that more callsigns will end in ‘1’ and, later in the day, with ‘9’. Then there are the ‘prestige’ flights – the ‘001’s’, ‘100’s’etc. To say that companies are reluctant to change one particular flight number, let alone their numbering system, is an understatement. Most quote the problems of timetables having already been printed, tickets and publicity material, brochures etc., and flatly refuse to change a number – even if it operates in conflict with an identical number of another company – at least until the winter or summer schedule change. Some refuse to change at all.

Are we trying to solve a simple problem of poor RTF discipline with very technical and complex solutions ?

Again, the answers to the questionnaire in 1979 indicate that poor RTF discipline made the problem worse but that it was not the root cause of the problem. No matter how good your RTF discipline is, when the traffic situation is busy it is much more likely that pilots and controllers will become confused if the companies are operating with similar flight numbers. If these flight numbers are also numbers that can be used for headings, levels or squawks the situation gets even worse.

‘Very technical and complex solutions’ – the IFALPA proposal to convert flight numbers( of those companies who wished to use that method of RTF identification) directly to an alphabetic derivative is neither very complex or very technical. Most aviation organisations now use some form of computer assistance and simple programs allow conversion from one format to the other merely by typing in one of the formats. Even without computer assistance conversion only involves reading from a table, which any airline clerk could do. ATC would not be involved in any conversations. As far as the controller would be concerned the callsign would be the alpha numeric format, spoken for 99% of the time as company designator + 2 letters ( e.g. ‘Speedbird Mike Echo’). All reference to that flight within ATC and between ATC and the airline would be in the alpha numeric format. This is not a ‘very technical or complex solution’.

Can some problems be solved with equipment ?

It is the view of SC 1 that, at least for the foreseeable future, this is not a problem which can be solved by equipment.

Other possibilities

In view of the difficulty of finding an answer to these problems, perhaps the ides that one new method will provide a solution should be reviewed. Perhaps more choice in the method of filing callsigns is necessary. However, it is considered most unlikely that airlines will stop using the ‘trip number’ system. On particular system of ‘domestic use only’ callsigns has been operating successfully in the UK for many years now. Other countries may have similar arrangements. Provided these reduce callsign confusion and number saturation they should be encouraged.

Perhaps system could be developed whereby short-haul international flights use one method of filing their callsigns and international flights use another system.

Bearing in mind that a major problem is number saturation, any solutions developed should utilise an increase in letters rather than numbers. Solutions should also be capable of handling suffixes.

On a purely technical basis, when faced with 2 companies operating in the same airspace simultaneously, and using identical trip numbers, one company could be required to repeat its designator after the trip number (e.g. Danair 123 Danair).

To conclude

It is considered that there most definitely is a problem, not the least of which is number saturation.

Neither the callsign confusion nor the number saturation problems are simple to resolve.

There is no solution to be found by the use of equipment at present.

It seems likely that no single solution will resolve these problems. The system proposed by IFALPA could be used in conjunction with the present trip number system to relieve some of the problems. Effort is still needed to try to produce solutions.

It is recommended that:

Any alpha numeric system considered for use must :

  1. be capable of abbreviations;
  2. not require a large proportion of the callsigns to be used in any one area to end in the same character;
  3. be suitable for display on existing and planned electronic data displays (EDD’s);
  4. use more letters than numbers.

Any solution proposed should be capable of showing amendments from a previously filed flightplan (e.g. comparable to the present ‘Q’ suffix within Europe when re-routeing to avoid excessive delays).

Considerations should be given to the possibility of having separate callsign systems for domestic, international long haul, and intercontinental flights.

Last Update: September 20, 2020  

December 1, 2019   813   Jean-Francois Lepage    1987    

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