SMA PLT HAS RADIO PROBLEM; FAILS TO CANCEL IFR.

Narrative

WHILE ON AN IFR FLT PLAN FROM DTO TO KERRVILLE; TX; I WAS IN CLR CONDITIONS UNDER HOUSTON CTR'S CTL; 5 MI N OF THE ARPT AT KERRVILLE. I WAS CLRED FROM 5000 FT TO 4000 FT WHEN I APPARENTLY LOST CONTACT WITH HOUSTON CTR. THEY HAD JUST TOLD ME TO DSND TO 4000 FT AND ASSIGNED A VISUAL APCH AND TO CANCEL MY IFR FLT PLAN WITH SAN ANGELO FSS. I REPLIED FIELD IN SIGHT AND TO CANCEL MY IFR FLT PLAN. I DID NOT KNOW THAT THEY HAD NOT RECEIVED MY MESSAGE. WHEN I GOT CLOSER TO THE FIELD AND TRIED TO CALL THE CTR AGAIN AND TELL THEM THAT I WAS GOING TO UNICOM FREQ; BUT WAS UNABLE TO CONTACT HOUSTON CTR. I WAS UNABLE TO CONTACT UNICOM AND LANDED UNEVENTFULLY. I LEARNED THE NEXT DAY THAT ATC HAD CALLED THE FBO AND SAID THAT I HAD NOT CANCELLED FLT PLAN. I BELIEVED THAT I DID CANCEL FLT PLAN AND WAS SHOCKED. I HAVE BEEN FLYING SINCE 1956 (25 YRS AS AN MIL PLT) AND FLYING LIGHT ACFT DURING AND SINCE MIL RETIREMENT. I HAVE NEVER HAD AN INCIDENT; ACCIDENT; VIOLATION AND HAVE NEVER FILLED OUT ANY PAPERWORK SUCH AS THIS IN THE MIL OR IN CIVILIAN FLYING. FLYING SAFETY HAS ALWAYS BEEN A PRIORITY TO ME AND I ALWAYS ATTEMPT TO ADHERE TO SAFETY AND FAA RULES AND REGS.