What was found
THE FLIGHT CREW REPORTED AN "ADS-B FAIL" MESSAGE ON BOTH RTU UNITS AND "TCAS FAIL" MESSAGES ON MFD. WHEN USING BOTH RTS'S ON TRANSPONDER 1, RTU 2 SCREEN REVERTS TO DASHES "------". THE MAINTENANCE TEAM REMOVED THE NO1 COMMUNICATIONS UNIT AND INSTALLED REPAIRED COMMUNICATIONS UNIT. OPERATIONAL CHECKS WERE SATISFACTORY. THE MAINTENANCE TEAM ALSO REPLACED THE NO1 INTEGRATED NAVIGATION UNIT WITH A REPAIRED UNIT. OPERATIONAL CHECKS WERE SATISFACTORY.