and specifically codes in Spain with LE. For example, New York's John F. Kennedy airport is KJFK while Goose Bay Canada's airport is identified as CYYR and Bilbao in Spain as LEBB. Some irregular four-letter codes, not assigned by ICAO, do exist and appear usually in meteorological reports. Examples for some common three-letter-groups used in AFTN addresses in order to identify an organization or service: Therefore the address LEBBYNYX indicates the NOTAM office of Bilbao Airport, Spain. 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