SMA PLT INSTRUCTOR WITH TRAINEE LANDED WITHOUT CLRNC; CITING RADIO FAILURE. FLC ACKNOWLEDGE THEY WERE UNAWARE OF CORRECT TIME; ASSUMING TWR WAS CLOSED; WHEN THEY OBSERVED LIGHT GUN SIGNALS. FLC STATES THEY SHOULD HAVE HAD GREATER SITUATIONAL AWARENESS.

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I WAS ON A NIGHT TRAINING FLT WITH A STUDENT WHEN THIS OCCURRED. MY STUDENT AND I WERE DISCUSSING THE FLT INSIDE BEFORE WE WENT OUT TO THE AIRPLANE. WE BOTH LOST TRACK OF TIME. AFTER PREFLT; WE CONTACTED TWR AND PROCEEDED TO THE RWY AND TOOK OFF. I WAS DISCUSSING THE TKOF WHEN THE TWR INFORMED ALL TFC THAT THE ATIS CHANGED. I MISUNDERSTOOD THE ANNOUNCEMENT THAT TWR MADE. I THOUGHT THAT THEY HAD JUST CLOSED FOR THE NIGHT. WE RETURNED TO THE ARPT AT XA45 PM THINKING THAT IT WAS ALREADY AFTER XB00 PM; WHEN THE TWR CLOSED. MY STUDENT WAS UNDER THE HOOD; SO I WAS MAKING ALL RADIO CALLS. I MADE A CALL TO EXECUTIVE TFC UPON REACHING DOWNWIND AND PROCEEDED TO CALL BASE AND FINAL APCH. BECAUSE THERE WAS NO RESPONSE ON THE FREQ; WE ASSUMED NO OTHER TFC WAS IN THE AREA USING CTAF. JUST BEFORE TURNING FINAL; I NOTICED ACFT Y TURNING FINAL INSIDE OF US (WE WERE ABOUT 4 MI OUT). WE THEN MADE S- TURNS FOR SEPARATION AND PROCEEDED TO LAND. ONCE WE WERE ON THE RWY; I LOOKED TOWARD THE TWR; NOTICED THEM GIVING US LIGHT SIGNALS TO EXIT THE RWY. I REALIZED AT THIS TIME WE HAD A RADIO FAILURE AND TWR WAS STILL OPEN. I CONTACTED TWR ON OUR OTHER RADIO. OUR FIRST RADIO WAS BROADCASTING; BUT NOT RECEIVING. OUR CALLS HAD BEEN HEARD BY TWR BUT WE COULDN'T HEAR THEIR RESPONSE. I THINK THAT IF I HAD KEPT BETTER TRACK OF TIME AND PAID MORE ATTN TO TWR COMS THIS WOULD HAVE BEEN AVOIDED.