In this advanced chapter, we are going to look into different versions and evolution of the ADS-B.
Since the beginning of ADS-B, there have been three different versions (to my knowledge) implemented. The major reason for these updates is to enable more information (types of data) in ADS-B. Documentations on these versions and differences are quite far from user friendly. They are always presented in a very scattered fashion. Even the official
ICAO_9871 document is confusing to read. I am going to try my best to put the pieces together in this chapter.
There are three versions implemented so far, starting from Version 0, then Version 1 around 2008 and Version 2 around 2012. Major changes in Version 1 and Version 2 are listed as follows:
Version 0 to
Added Type Code 28, 19, and 31 messages
TC=28: Aircraft status - Emergency/priority status and ACAS RA Broadcast
TC=29: Target state and status
TC=31: Operational status
Introduced the “Navigation integrity category (
NIC)” and “Surveillance integrity level (
SIL)” in addition to the “Navigation accuracy category (
NAC)” from the
Type Code and an NIC Supplement bit (
NICs) is used to define the NIC
NIC Supplement bit included in
The ADS-B version number is now indicated in operation status message
Version 1 to
Re-defined the structure and content of
Introduced two additional NIC Supplement Bit
NICa is defined in operational status messages (
NICb is defined in airborne position messages (
NICc is defined in operational status messages (
Introduced an additional “Horizontal Containment Radius (
There are two steps to check the ADS-B version, this is due to the fact that ADS-B
Version 0 is not included in any message.
Step 1: Check whether an aircraft is broadcasting ADS-B messages with
TC=31 at all. If no message is ever reported, it is safe to assume that the version is
Step 2: If messages with
TC=31 are received, check the version numbers located in the 41-43 bit of the payload (or 73-75 bit of the message).
After identifying the right ADS-B version for an aircraft (which does not change often), one can decode related
TC=31 messages accordingly.