FAQ n.44273

The requirements are described in AMC 20-24 and CS-ACNS. 

Note that:

• Position and velocity information must come from the same source.
• ETSO-C129A is the minimum equipage qualification in Europe. 
• For compliance with CS-ACNS, the applicable ETSOs (C129a/196/145/146) alone does not guarantee that the unit is suitable as an ADS-B position source. Further demonstration is required (see in particular AMC1 ACNS.D.ADSB.070 and .080).
• The System Design Assurance (SDA) parameter can be set to 2 without analysis if the GPS and ADS-B unit are both approved (to either ETSO C129a, C196(), C145(), C146()) and directly connected (i.e. direct wiring from GPS to receiver with no routing through other equipment). Aircraft with other architectures require a system safety analysis to set the SDA.