Narrative:

I was flying a C172. The flight was on an IFR clearance. I was sitting right seat providing instrument instruction to a student plting the plane from the left seat. WX was VMC -- high then overcast with visibility +10 mi. We were flying direct grand strand (cre) VOR at 4000 ft MSL and were approximately 15 mi from cre when we received instruction to 'descend to 3000 ft, maintain 3000 ft to the cre VOR, cleared for the twin city (5j9) VOR/DME-a approach.' I acknowledged 'leaving 4000 ft for 3000 ft, maintain 3000 ft to the VOR, cleared for the approach.' we descended to 3000 ft. While level at 3000 ft, I briefed my student about the turns and dscnts that would be required once crossing cre to begin the approach. Before reaching cre, however, we were instructed to climb and maintain 4000 ft to the VOR. How this climb instruction was issued and how we acknowledged the instruction are the key elements that created a misunderstanding that led to an altitude deviation. We were on approximately a 120 degree heading. To begin the approach, we needed to turn left to intercept and track the 340 degree radial outbound from crew. The initial approach segment has a minimum altitude of 1800 ft. We crossed crew, and I instructed my student to turn left to 320 degrees. He did so, and as we were intercepting the radial to track outbound from cre to the 5j9 airport, I instructed my student to initiate a descent to 1800 ft. While passing through about 3300 ft, the controller informed us that we had been instructed to maintain 4000 ft until cleared for lower. Apparently he had some traffic at 3000 ft. I stopped our descent at 3200 ft and initiated a climb back to 4000 ft. After just a few (10-15) seconds, the controller cleared us to continue the descent. Apparently the traffic was not nearby, and no traffic conflict was imminent.

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Original NASA ASRS Text

Title: A C172 INSTRUCTOR AND STUDENT, WHILE MAKING A VOR DME APCH, PREMATURELY STARTED THEIR DSCNT TO THE INITIAL ALT, AFTER ATC HAD CLRED THEM TO MAINTAIN 4000 FT.

Narrative: I WAS FLYING A C172. THE FLT WAS ON AN IFR CLRNC. I WAS SITTING R SEAT PROVIDING INST INSTRUCTION TO A STUDENT PLTING THE PLANE FROM THE L SEAT. WX WAS VMC -- HIGH THEN OVCST WITH VISIBILITY +10 MI. WE WERE FLYING DIRECT GRAND STRAND (CRE) VOR AT 4000 FT MSL AND WERE APPROX 15 MI FROM CRE WHEN WE RECEIVED INSTRUCTION TO 'DSND TO 3000 FT, MAINTAIN 3000 FT TO THE CRE VOR, CLRED FOR THE TWIN CITY (5J9) VOR/DME-A APCH.' I ACKNOWLEDGED 'LEAVING 4000 FT FOR 3000 FT, MAINTAIN 3000 FT TO THE VOR, CLRED FOR THE APCH.' WE DSNDED TO 3000 FT. WHILE LEVEL AT 3000 FT, I BRIEFED MY STUDENT ABOUT THE TURNS AND DSCNTS THAT WOULD BE REQUIRED ONCE XING CRE TO BEGIN THE APCH. BEFORE REACHING CRE, HOWEVER, WE WERE INSTRUCTED TO CLB AND MAINTAIN 4000 FT TO THE VOR. HOW THIS CLB INSTRUCTION WAS ISSUED AND HOW WE ACKNOWLEDGED THE INSTRUCTION ARE THE KEY ELEMENTS THAT CREATED A MISUNDERSTANDING THAT LED TO AN ALTDEV. WE WERE ON APPROX A 120 DEG HDG. TO BEGIN THE APCH, WE NEEDED TO TURN L TO INTERCEPT AND TRACK THE 340 DEG RADIAL OUTBOUND FROM CREW. THE INITIAL APCH SEGMENT HAS A MINIMUM ALT OF 1800 FT. WE CROSSED CREW, AND I INSTRUCTED MY STUDENT TO TURN L TO 320 DEGS. HE DID SO, AND AS WE WERE INTERCEPTING THE RADIAL TO TRACK OUTBOUND FROM CRE TO THE 5J9 ARPT, I INSTRUCTED MY STUDENT TO INITIATE A DSCNT TO 1800 FT. WHILE PASSING THROUGH ABOUT 3300 FT, THE CTLR INFORMED US THAT WE HAD BEEN INSTRUCTED TO MAINTAIN 4000 FT UNTIL CLRED FOR LOWER. APPARENTLY HE HAD SOME TFC AT 3000 FT. I STOPPED OUR DSCNT AT 3200 FT AND INITIATED A CLB BACK TO 4000 FT. AFTER JUST A FEW (10-15) SECONDS, THE CTLR CLRED US TO CONTINUE THE DSCNT. APPARENTLY THE TFC WAS NOT NEARBY, AND NO TFC CONFLICT WAS IMMINENT.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.