A CFI AND HIS STUDENT MISS AND APCH ON AN IFR FLT PLAN. CANCELLATION OF THE IFR FLT PLAN TURNS INTO A PROB.

Narrative

WHILE ACTING AS A CFI IN A C172 WITH A PVT PLT WORKING ON AN INST RATING; A FLT PLAN WAS FILED FROM 23N TO OXC; IFR. DURING THE FLT; WE REQUESTED THE NDB 18 OXC FULL APCH INTO OXC ARPT AND WAS GRANTED THE REQUEST. DURING THE APCH; BEFORE REACHING THE IAF; THE APCH CTLR CALLED OUT THAT RADAR COVERAGE WAS LOST AND THAT WE SHOULD CANCEL OUR IFR FLT PLAN EITHER IN THE AIR OR ON THE GND. WE HAD ALREADY MADE THE DECISION THAT WE WOULD CANCEL ON THE GND; AND; IN MY OPINION; IS SAFER THAN CANCELING WHILE AIRBORNE. UPON TURNING FOR THE FINAL APCH; INSIDE THE FAF; MY INST STUDENT DECIDED HE COULD NOT MAKE THE LNDG SAFELY AND EXECUTED A GAR. WE WERE IN VFR CONDITIONS AND DECIDED TO MAKE L TFC TO RWY 18 BY EXECUTING A L TURN ONTO THE DOWNWIND. UPON DOING THIS; A PERSON WAITING TO TAKE OFF COMPLAINED THAT WE WERE TAKING TOO MUCH TIME TO LAND AND FURTHER CALLED APCH CTL TO ADVISE THEM THAT WE WERE DOING TOUCH AND GOES. I TRIED TO CANCEL MY IFR FLT PLAN IN THE AIR; AND WAS TOLD TO CALL A NUMBER WHEN I GOT ON THE GND. I TRIED TO CALL THE NUMBER AND GOT NO ANSWER. I FURTHER CALLED FSS (1-800-WX-BRIEF) TO CANCEL AND INQUIRE ABOUT THE NUMBER I WAS SUPPOSED TO CALL. FSS CALLED THE NUMBER FOR ME AND VERIFIED THAT EVERYTHING WAS FINE AND NOT TO WORRY. IT WAS MY UNDERSTANDING THAT IT WAS OUR AIRSPACE WHEN CLRED FOR THE FULL NDB APCH INTO THE ARPT AT OXC AND CANCELED WHEN WE GOT ON THE GND. WHEN TRAVELING BACK LATER; APCH CTL INFORMED ME THAT I WOULD HAVE TO CALL AGAIN TO DISCUSS THE PROB. THEY SOMEHOW NEVER RECEIVED MY CANCELLATION FROM FSS.