This change to DO-289 mainly clarifies the definitions of several parameters transmitted by aircraft in ADS-B messages. These parameters provide information to the recipient of the ADS-B message about the quality of the transmitted aircraft position. The change has been developed in a manner that reflects typically available aircraft position sources and should not impact ADS-B equipment previously certified using RTCA DO-260A for 1090 MHz Extended Squitter or RTCA DO-282A for the Universal Access Transceiver (UAT).