Aeronautical Fixed Telecommunication Network

The Aeronautical Fixed Telecommunication Network (AFTN) is a worldwide system of aeronautical fixed circuits provided, as part of the aeronautical fixed service, for the exchange of messages and/or digital data between aeronautical fixed stations having the same or compatible communications characteristics. AFTN comprises aviation entities including: ANS (Air Navigation Services) providers, aviation service providers, airport authorities and government agencies, to name a few. It exchanges vital information for aircraft operations such as distress messages, urgency messages, flight safety messages, meteorological messages, flight regularity messages and aeronautical administrative messages.

Communications infrastructure

Station address format

AFTN addresses are 8 characters long. They consist of the 4-letter ICAO station code with a 4-letter facility code appended. Facility code ZTZX refers to "Control tower"ZPZX refers to "ATS Reporting Office"ZQZX refers to "Area Control Center"YNYX refers to "Notam Office"YDYX refers to "Airport Manager"YZYX refers to "Met Data Bank"YMYX refers to "Local Met Office"ZRZA refers to "Ridar"

Message content

AFTN messages can be given a message priority to ensure best use of the system. The priority indicators and their meanings are shown in the following table:

The AFTN system is backwards compatible with older transmission technology as many member states do not upgrade their AFTN centers fast enough. The message format betrays the extensive use of radioteletype links in the past. A typical message would look like:

ZCZC LAA005 12032000 DD OPKCZQZX 1209000 OPSTZQZX MESSAGE NNNN

The ZCZC is the start of message indicator that was originally used by torn-tape stations. The "Z" and "C" characters do not normally occur together in standard text and provide a unique character pattern for automating the identification of the beginning of a message. The NNNN is the end of message indicator that also has a character pattern that is not found in standard text.

The message routing is easily automated by general purpose computers. Teletype communication with airline operators is sometimes maintained by having a connection to the IATA Type B messaging networks which use a 7 character address. The whole communications system is still rooted in the 'official' nature of radio teletypes.

The older tape stations (and perhaps newer ones) also included a bell that could be rung by using a set character code. The purpose of the bell was to allow the sender to alert the receiving operator of a high priority message such as an SS message. It was also possible to insert spacing between bell rings. With care and persistence, you could compose a musical tune to play to far distant stations. Jingle bells was a favourite. A particularly clever 'author' could combine the tune with an image such as a Christmas tree. The skill for this was often learnt on those long night watches when little traffic was in the air.

Each country within the network has it airports and aerodrome reporting location addresses beginning with a letter. For instance the letter K, is the first letter of the four letter ICAO address location within the United States. The first letter for a Canadian aerodrome, or airport address, begins with the letter C.

Other airport required reports are also transmitted through the AFTN, on daily and hourly intervals like flight plans, NOTAM's (notices to airmen), and AIRAD's (Airfield Advisories). For example, a message originated at New York's John F. Kennedy airport would be KJFK. Goose Bay Canada's airport originated messages would be identified as CYYR.

Further reading

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