As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) AFTER TAKEOFF THE CREW WAS ADVISED BY ATC THEY WERE NOT RECEIVING TRANSPONDER INFO FROM THE FLIGHT. THE FLIGHT RETURNED AND LANDED NORMALLY. THE CREW DID NOT DECLARE ANY EMERGENCY BUT THE EMERGENCY RESPONSE VEHICLES ATTENDED THE LANDING. MRC1 NIM REPLACED IAW AMM 34-02-04.