PA28 PLT AND INSTRUCTOR STARTED AN INST APCH TO DTS WITHOUT BEING CLRED FOR THE APCH.

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ON A WEEKEND AFTERNOON; I WAS TAKING AN INST PROFICIENCY CHK (IPC) WITH A CFII. WE WERE IN VFR CONDITIONS DURING DAYTIME WITH GOOD VISIBILITY. AFTER PRACTICING PARTIAL PANEL; UNUSUAL ATTITUDES; ETC; WE ELECTED TO DO AIR WORK AROUND THE CRESTVIEW; FL; VOR (CEW). THE INTENT WAS TO DO HOLDING AND THEN SHOOT A PRACTICE APCH (VOR-A) INTO CRESTVIEW ARPT UNDER VFR. NEARING THE VOR; WE DETERMINED THAT A THUNDERSHOWER WAS IN PROGRESS ON THE HOLDING SIDE OF THE VOR AND WE WOULD BE UNABLE TO COMPLETE THE PLANNED AIR WORK AT THAT LOCATION. AT THE SUGGESTION OF THE CFII; I TOLD PENSACOLA APCH (WHO HANDLES EGLIN AFB APCH'S AIRSPACE ON WEEKENDS) THAT WE WOULD LIKE TO PROCEED S DIRECT TO DTS NDB (CO-LOCATED AT THE DESTIN; FL; ARPT). AND EXECUTE A PRACTICE NDB APCH TO DESTIN ARPT UNDER VFR. THE CTLR TOLD US THAT WAS APPROVED AND TO MAINTAIN AT OR ABOVE 2500 FT. SEVERAL MINS LATER; WE ASKED FOR CONFIRMATION THAT WE WERE CLRED THROUGH CLASS D AIRSPACE AT EGLIN AFB AND THE CTLR TOLD US THAT YES -- THAT WAS AFFIRMATIVE; HE ALREADY WORKED THAT OUT WITH EGLIN. HE ONCE AGAIN SAID TO MAINTAIN AT OR ABOVE 2500 FT. THE NDB APCH FOR RWY 32 INTO DESTIN ARPT HAS A FEEDER RTE FROM THE CRESTVIEW VOR (IE; WHERE WE WERE COMING FROM). THE PROC CALLS FOR A DSCNT FROM THE FEEDER RTE ALT TO 1600 FT ONCE PAST THE NDB (THE INITIAL APCH FIX) AND ESTABLISHED ON THE OUTBOUND LEG. THE OUTBOUND LEG AND PROC TURN IS OVER THE GULF OF MEXICO ON A SE COURSE OF 147 DEGS. THE CFII REMINDED ME TO START SLOWING DOWN AS WE APCHED THE NDB; IN ANTICIPATION OF EXECUTING THE APCH PROC. WHEN WE PASSED THE NDB; HE AGAIN PROMPTED ME TO FOLLOW PROC AS I DELAYED A FEW SECONDS BEFORE MAKING THE TURN TO 147 DEGS AFTER PASSING THE NDB. PER THE CHARTED PROC; I STARTED MY DSCNT DOWN TO 1600 FT OVER THE GULF OF MEXICO; SEBOUND ON THE OUTBOUND LEG. I REMEMBER HEARING PENSACOLA APCH INFORM A LEARJET THAT HIS TFC WAS A CHEROKEE (IE; US) S OF THE ARPT; AND THAT THE CHEROKEE WAS AT 1700 FT. A MOMENT LATER; I WAS ABOUT TO START THE PROC TURN WHEN PENSACOLA APCH ASKED ME TO 'SAY ALT.' I TOLD HIM 1600 FT. A FEW MOMENTS LATER; PENSACOLA APCH AGAIN ASKED ME TO SAY ALT; AND I RESPONDED WITH THE SAME ANSWER AS BEFORE; 1600 FT. I BELIEVE THE QUERY AND ANSWER REPEATED ITSELF A THIRD TIME. AFTER THE THIRD TIME; I TOLD HIM WE WERE AT 1600 FT; THE CTLR SAID THAT WE WERE SUPPOSED TO BE AT 2500 FT AND THAT HE HAD NOT CLRED US LOWER. I RESPONDED THAT I WAS SORRY FOR THE MISUNDERSTANDING BUT I THOUGHT THAT WE WERE CLRED FOR THE NDB APCH. HE ABRUPTLY TERMINATED OUR PRACTICE APCH AND TOLD US TO PROCEED DIRECT TO DESTIN ARPT. HE ALSO SOUNDED QUITE IRRITATED. WE PROCEEDED DIRECT DTS; CONTACTED CTAF A FEW MINS LATER; AND LANDED. IT IS POSSIBLE THAT WE CAUSED A TFC ALERT (BTWN US AND THE LEARJET) BUT I DO NOT KNOW THIS FOR A FACT; AS HE DIDN'T SAY. IN FACT WE WERE IN ERROR BY DSNDING TO 1600 FT; THERE WERE A COUPLE OF FACTORS. FIRST; IT WAS AMBIGUOUS (IN RETROSPECT) TO BE TOLD TO MAINTAIN AT OR ABOVE 2500 FT AND ALSO TO BE CLRED FOR A PRACTICE NDB APCH INTO DESTIN (VFR). OBVIOUSLY AT SOME POINT WE WOULD HAVE TO START OUR DSCNT...AND STARTING THE DSCNT AS PUBLISHED SEEMED TO BE THE RIGHT THING TO DO. IT ALSO WOULD HAVE BEEN HELPFUL IF THE CTLR HAD SAID; 'MAINTAIN AT OR ABOVE 2500 FT FOR TFC' (IE; A REASON FOR THE INSTRUCTION) OR 'MAINTAIN 2500 FT UNTIL ESTABLISHED INBOUND' (IE; A PLACE WHERE/WHEN WE COULD START OUR DSCNT). A SECOND FACTOR WAS HAVING A CFII ONBOARD WHO WAS URGING ME TO 'FLY THE PROC' AND WHO WAS SOMEWHAT OF A DISTR BY TALKING CONTINUOUSLY. HAD A CFII NOT BEEN ONBOARD; I WOULD PROBABLY HAVE BEEN MORE AGGRESSIVE ABOUT CLARIFYING THE INTENTIONS OF THE CTLR AND I ALSO WOULD HAVE BEEN LESS DISTRACTED. A THIRD CONTRIBUTING FACTOR WAS THAT THERE WAS A COM PROB WITH PENSACOLA APCH'S AUDIO (PENSACOLA APCH IS LINKED VIA REMOTE RADIO TO THE EGLIN AFB AREA; WHICH IS ABOUT 50 NM TO THE E). THE CTLR'S XMISSIONS SOMETIMES 'CUT OUT' PART-WAY THROUGH SENTENCES. I KNOW IT WAS NOT OUR RADIO(S) BECAUSE SEVERAL PLTS ASKED FORREPEAT INSTRUCTIONS AND TOLD HIM THAT HE WAS 'CUTTING OUT.' IT IS THEREFORE POSSIBLE THAT WE DID NOT HEAR SOME PART OF AN EARLIER XMISSION. FINALLY; VFR PRIVILEGES HAD JUST BEEN GRANTED IN THE NAS A FEW DAYS PREVIOUS; AND CTLRS IN THE VICINITY OF EGLIN AFB MAY HAVE BEEN SOMEWHAT 'ON EDGE' AND MUCH LESS WILLING TO ACCOMMODATE ANY PERCEIVED DEVS FROM EXPECTED BEHAVIOR. MY CFII TOLD ME THIS WK THAT HE TALKED TO A COMMERCIAL AVIATOR WITH OVER 30 YRS EXPERIENCE AND IT WAS THEIR OPINION THAT WE DID WHAT SHOULD HAVE BEEN EXPECTED BY THE CTLR.