PIPER PLT RPTS CTAF FREQUENCY ERROR ON COMMERCIAL CHART FOR TZT.

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EXECUTING PRACTICE GPS 18 APCH TO BELLE PLAINE; IA (TZT). USING FAA INSTRUMENT APCH CHARTS AND NOTICED THE UNICOM FREQUENCY WAS 122.9. I'VE GIVEN INSTRUCTION FOR MANY YEARS IN THIS AREA AND THE UNICOM HAS ALWAYS BEEN 122.8. WE WERE RECEIVING RADAR ADVISORIES FROM CEDAR RAPIDS APCH AND ASKED THEM ABOUT THE UNICOM FREQUENCY. THEY FIRST SAID 122.8 BUT THEN SAID 122.9. DIDN'T SEE ANY NOTAM OR RECEIVE ANY NOTICE THROUGH FAASAFETY.GOV ABOUT ANY FREQUENCY CHANGE. ALSO; THE PLT CONTROLLED LIGHTS ARE STILL ON 122.8. IN MY VIEW THIS MAKES TZT A 'HOTSPOT' WITH GREAT POTENTIAL FOR CONFLICTS BETWEEN AIRPLANES.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE MAIN COMPLAINT IS THAT THE CTAF FREQ HAD CHANGED AT TZT WITHOUT ANY NOTIFICATION. PLTS WHO FLY FREQUENTLY OFTEN RECALL FREQUENCIES FROM MEMORY WHICH COULD ALLOW TWO ACFT TO BE ANNOUNCING POSITIONS ON DIFFERENT FREQUENCIES. RPTR FEELS THESE CHANGES SHOULD BE WIDELY DISSEMINATED THROUGH LONG TERMED NOTAMS AND AVIATION SAFETY FORUMS.