Aeronautical Fixed Telecommunication Network - AFTN Message Format

AFTN Message Format

The message format of AFTN messages is defined in ICAO Annex 10 Aeronautical Telecommunications Volume II.

AFTN messages consist of a Heading', the Message Text and a message Ending.

The message Heading comprises a Heading Line, the Address and the Origin. The Heading Line comprises the Start-of-Message Signal which is the four characters ZCZC, the Transmission Identification, an Additional Service Indication (if necessary) and a Spacing Signal.

The AFTN Address comprises Alignment Functions, a two-letter Priority Indicator depending on the message category and an eight-letter group (Addressee Indicator). The first four letters of the eight-letter group is a Location Indicator indicating the place of destination. The following three-letter group indicates the organization or function addressed (for instance aeronautical authority, service or aircraft operating agency). The last letter of the eight-letter represents a department, division or process within the organization/function addressed.

The Origin consists of message Filing Time (six-digit date-time-group), the Originator Indicator (eight-letter group) identifying the message originator, a Priority Alarm (used only in teletypewriter operation for Distress Messages) and Alignment Functions.

The Message Text ends with the End-of-Message Signal, which is the four characters NNNN. The Ending itself comprises twelve letter shift signals which represent also a Message-Separation Signal.

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 120900 OPSTZQZX MESSAGE TEXT NNNN

Explanations:

• The first three lines in the example AFTN message above represent the Heading of the message.
• ZCZC LAA005 12032000 is the Heading Line in which ZCZC is the Start-of-Message Signal. 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. LAA005 refers to the Transmission Identification and 12032000 is an Additional Service Indication.
• The second line DD OPKCZQZX is the Address of the message. DD represents the Priority Indicator for the message category(an Urgency Message in this cases). OPKCZQZX is the eight-letter group identifying the addressee. OPKC refers to Karachi/Jinnah Intl, Pakistan. ZQZ refers to a Centre in Charge of Flight Information Region or Upper Flight Information Region'. In other words the addressee is Karachi Area Control Centre or Karachi Flight Information Centre. The last character X indicates that an explicit identification of the organization or function addressed is not required. So the X is just used to complete the originator address.
• The third line 120900 OPSTZQZX represents the Origin of the message. 120900 refers to the date-time-group and means the twelved day of month at time 09 o'clock UTC. OPSTZQZX is the originator of the message where OPSTZQZX refers to Area Control Centre or Flight Information Centre at Sialkot, Pakistan.
• The example does not give an explicit MESSAGE TEXT. In reality the contents of the message is included here.
• The Ending of the message is indicated by NNNN which is the End-of-Message Signal that also has a character pattern that is not found in standard text.
• The Alignment Functions and letter shift signals mentioned above are not visible in AFTN messages.

The message routing is easily automated by general purpose computers. Teleprinter 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 radioteletypes.

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.

Other airport required reports are also transmitted through the AFTN, on daily and hourly intervals like flight plans, NOTAMs (notices to airmen), and AIRADs (Airfield Advisories).