As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE ON THE FLIGHT FROM TNCC TO KOPF, FLIGHT CREW EXPERIENCED A TRANSPONDER & CAPTAIN'S SIDE INSTRUMENT FAILURE AFTER REACHING FL190. AIRCRAFT RETURNED TO TNCC AND HAD AN UNEVENTFUL LANDING. AFTER TROUBLESHOOTING BY MAINTENANCE THE AIR DATA COMPUTER WAS FOUND AT FAULT. LOG ENTRY: ABOVE FL190 THE TRANSPONDER FAILS AND INSTRUMENTS ON THE CAPTAIN SIDE FAILS ALSO.