POSSIBLE AIRSPACE VIOLATION; INCURSION INTO RESTR AIRSPACE R-2519 S OF NTD BY A C172 WITH FAILED RADIOS DUE TO SMOKE IN COCKPIT S OF VTU.

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WE HAD DEPARTED OXR ON THE RETURN LEG OF A 2 LEG TRAINING FLT AND HAD JUST REACHED CRUISING ALT OF 5500 FT MSL. WE HAD CONTACTED PT MAGU APCH TO REQUEST FLT FOLLOWING TO CARLSBAD/PALOMAR ARPT (CRQ). WE HAD JUST BEEN GIVEN A HDOF FREQ AND WERE IN THE PROCESS OF COMMUNICATING ON THAT NEW FREQ. THE MIKE WAS KEYED AND THE COCKPIT WAS QUICKLY FILLED WITH ACRID SMOKE THAT SMELLED OF BURNING ELECTRONICS. THE CFI THAT I WAS WITH IMMEDIATELY TURNED OFF THE AVIONICS MASTER AND WE PROCEEDED TO EXECUTE THE 'ELECTRICAL FIRE INFLT' CHKLIST AND TURNED BACK TOWARDS OXNARD WHILE NORDO. WE WERE ABLE TO GET THE XPONDER BACK ON AND SQUAWKED 7700 BUT DID NOT WANT TO ATTEMPT TO USE A RADIO SINCE WE WERE NOT SURE WHAT WAS WRONG. WE RECEIVED LIGHT SIGNALS FROM THE OXNARD TWR AND LANDED UNEVENTFULLY. AFTER SECURING THE PLANE AND TELEPHONING THE TWR; WE REVIEWED THE CHARTS AND I BELIEVE THAT WE FLEW THROUGH RESTR AIRSPACE R-2519 WHICH IS S OF PT MAGU NAS (NTD). THIS WAS PROBABLY ONE OF THE BETTER TRAINING FLTS THAT I HAVE EXPERIENCED; AS IT ALLOWED ME TO SEE THE IMPORTANCE OF A NUMBER OF THINGS INCLUDING CRM; SITUATIONAL AWARENESS; AND EMER PROCS.