The purpose of this Circular is to inform OPMET data (Operational Meteorological Data) transmitters/intermediaries and users of implementing the ICAO IWXXM model from 05 NOV 2020.

According to Amendment No 78 to ICAO Annex 3 (Meteorological Service for International Air Navigation), as of 05 NOV 2020 the IWXXM model (ICAO Meteorological Information Exchange Model) will be used for transmitting OPMET messages additionally to the current TAC format (Traditional Alphanumeric Code form).

For OPMET data (METAR/SPECI, SIGMET, AIRMET, TCA, VAA and SWXA) the implementation of IWXXM model is mandatory from 05 NOV 2020 and it is in accordance with ICAO ASBU, B1-AMET (Aviation System Block Upgrades, Advanced Meteorological Information).

In accordance with the planned Amendment No 79 to ICAO Annex 3 (Meteorological Service for International Air Navigation), it is recommended to use the IWXXM model for transmitting the SIGWX chart as of 04 NOV 2021. The transition from TAC format to IWXXM model is a prerequisite for ICAO SWIM (System Wide Information Management).

IWXXM technical specifications are stated in WMO (World Meteorological Organisation) Document No 306, Volume I.3, Part D (Representation Derived from Data Models) and implementation guide in ICAO Doc 10003 (Manual on the ICAO Meteorological Information Exchange Model, ed 2 2019).