FAS DB: Final Approach Segment Data Block

FAS DB: Final Approach Segment Data Block

GNSS approach procedures use an algorithm called Cyclic Redundancy Check (CRC) to ensure that whatever data is provided by an ANSP is correctly translated into the avionics guidance functions in the aircraft.  The FAS DB tool packs the 3D final approach track into a specific data record and calculates the CRC.  The CRC function is then used at each point in the data chain to check that no data has changed.

The Final Approach Segment Data Block (FAS DB) is an online tool especially designed for satellite-based augmentation systems’ (SBAS) final approach segment data block calculations. It is primarily used to generate a cyclic redundancy check (CRC) value for FAS DB based on user-input data.

The tool checks the format and range of the data entered before making the CRC calculation. The results (CRC and non-CRC-wrapped data) can be copied, printed or exported in a binary format for subsequent use or put into PDF format to support RNP APCH publication in AIP.


EUROCONTROL provides this tool to all interested parties free of charge. Access to the tool does not require authentication.

Access tool


Using the tool supports the publication of Required Navigation Performance approach (RNP APCH) to Localizer Performance with Vertical guidance (LPV) minima. It ensures that the AIS provider submits all the LPV specific data required by a Data House for coding the procedure into a navigation database in ARINC 424 format.

The FAS DB format and the CRC algorithm meet all the ICAO Annex 10 requirements and the tool has been comprehensively tested, using data from a number of sources including industry, the FAA and ICAO.

What's new?

Some of the improvements which come with version 3.0.1 include:

  • GAGAN and SDCM are now available as options in the list of potential SBAS systems supporting RNP APCH to LPV;
  • full compatibility with SBAS-CAT I operations (following the LPV200 declaration of service of EGNOS);
  • interface improvements with additional checks and warnings on input data.
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