UNAUTH PENETRATION OF CLASS D AIRSPACE BY INSTRUCTOR PLT AND STUDENT. UNAUTH LNDG TKOF; TOUCH AND GO; PERFORMED.

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APCHING SPACEPORT EXECUTIVE ARPT FROM THE S MADE 3 ATTEMPTS TO CONTACT TWR WITH NO RESPONSE. CHKING THE ARPT FACILITIES DIRECTORY WHILE WE CIRCLED I THOUGHT THE TWR WAS STILL OPEN AND TRIED THE TWR ONCE MORE WITH NEGATIVE RESULTS. I THEN SWITCHED TO THE LISTED UNICOM FREQ AND HEARD AN ACFT RPTING FINAL FOR RWY 36. I VISUALLY SIGHTED A CESSNA ON FINAL FOR RWY 36 AND ASSUMED TWR WAS CLOSED. I PROCEEDED MAKING ALL OF MY TFC CALLS ON THE UNICOM FREQ. AFTER A TOUCH AND GO I WAS CONTACTED BY ANOTHER ACFT AND TOLD TO CALL THE TWR. THE TWR SAID THEY HEARD ME AND HAD RESPONDED. THEY ALSO TOLD ME NEVER TO USE THE UNICOM FREQ; THAT IT IS FOR FBO'S. TFC SEPARATION WAS NEVER A PROB IN THIS SIT. I BELIEVE THAT ONLY FREQS TO BE USED TO SUPPORT FLT OPS SHOULD BE LISTED ON THE SECTIONAL CHARTS. ADMINISTRATIVE FREQS SHOULD BE (AND ARE) LISTED IN ARPT GUIDES AND THE AFD. AFTER THIS EVENT TOOK PLACE; I DISCUSSED IT WITH 3 OTHER CFI'S. ONE CFI WAS UNDER THE BELIEF; AS WAS I; THAT WHEN THE TWR IS CLOSED; USE THE LISTED UNICOM FREQ.