ARINC424 is an aeronautical specification developed and maintained by the industry which has been used for the exchange of navigation and communication data between commercial data suppliers and avionic system manufacturers for more than 30 years
It was created in the 70’s to meet the requirements of more complex embedded navigation systems (FMS) supporting evolving navigation techniques. The ARINC424 sets forth the air transport industry’s recommended standards for the preparation of airborne navigation system reference data files.
The first issue of the ARINC424 specification was officially published in May 1975. The version applicable in August 2010 is version 19, which was released on December 2008. The specification is maintained by the A424 committee which groups the major aeronautical actors involved in the different steps of the data production chain:
- ANSP & administrations
- Commercial data providers
- Avionic systems suppliers
- Aircraft manufacturers
The ARINC424 specifies a format of navigation (and communication) data based on text files containing lines of 132 alphanumeric characters. Section 4 “ARINC424 Records” and Section 5 “ARINC424 Fields” detail the textual structure and the type of alphanumeric characters which shall be used in order to represent aeronautical features. The picture below illustrates how an Airport can be expressed in ARINC424.
In addition to the description of the format, the ARINC424 specification also provides a series of rules (Business rules) explaining how the Aeronautical Information Publication should be interpreted (naming convention for waypoints for instance). One of the major chapters of the specification (Attachment 5) deals with the encoding of terminal procedures (SID, STAR, Approaches). The ARINC424 defines in particular the concept of Path&Terminators (elementary trajectories which are sequenced in order to represent a complete procedure) which is now more and more adopted outside the strict A424 community. As an example, the ARINC424 Path&Terminator concept is reused in the ICAO Performance-Based Navigation Manual.
The ARINC424 datasets are assembled by commercial data suppliers based on the public sources (AIPs). Custom data (also named tailored data) which is specific to the end-user, such as the Company Routes specified by an airline, is added to this in initial set of standard ARINC424 data. The ARINC424 text files are then converted into binary datasets by ground compilers (packing software) which are unique to each avionic system manufacturer; at this stage, the input ARINC424 dataset can be adapted to meet the specific requirements of a target Flight Management System. The resulting binary file is a navigation database which is unique per FMS manufacturer and per FMS type. The picture above illustrates the general data production chain, from the publication to the embedded system.
One of the main consequences of this process is that an airline operating a mixed fleet will have to manage and validate many different types of navigation databases every 28 days (the AIRAC cycle), which generates significant logistic effort and costs.