INSTRUCTOR PLT DECLARES AN EMER AFTER THE C172 WAS ICING UP IN A HOLDING PATTERN FOR AN INST APCH. THE ICING CAUSED THE ACFT'S SPD TO DETERIORATE AND MORE PWR WAS BEING APPLIED TO HOLD ALT. THE ICE CAME OFF AS THE ACFT DSNDED ON THE APCH.

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DEPARTED WICHITA ON LCL IFR CLRNC TO HUTCHISON TO COMPLETE AN INST COMPETENCY CHK WITH MY STUDENT. APPROX XX00 LCL TIME. CHKED WX WITH FSS APPROX XX00 LCL AND THEY SAID THAT THERE WERE NO RPTS; OR FORECAST OF ICE IN THE ICT/HUT AREA. FLEW TO HUT AT 3500 FT OR 4000 FT? WITH NO ICE BEING OBSERVED; BUT THERE WAS A LOT OF MOISTURE IN THE CLOUDS. WE HAD INITIALLY PLANNED TO JOIN THE ARC FOR VOR 3 APCH; BUT HUT DME WAS INTERMITTENT. WE REQUESTED DIRECT TO THE HUT VOR WITH ONE COMPLETE TURN IN HOLDING; THEN THE VOR 3 APCH. WHILE IN THE CLOUDS THE LNDG LIGHT WAS LEFT ON TO BETTER DETECT ICE ON THE WINDSHIELD IF IT SHOULD OCCUR; AND I WOULD VISUALLY INSPECT THE WINGS EVERY FEW MINS. MY STUDENT WAS WEARING A HOOD; SINCE WE OCCASIONALLY WOULD BE ON TOP BTWN LAYERS. REACHING HUT VOR WE ENTERED THE HOLD. JUST PRIOR TO ENTERING THE HOLD; I CHKED FOR ICE; AND THERE WAS NONE. (3500 FT.) AFTER THE ENTRY; AND HALFWAY ROUND THE FIRST FULL HOLDING PATTERN I NOTICED THAT THE AIRSPD WAS SLOWING AND THE STUDENT WAS GRADUALLY ADDING MORE PWR. I IMMEDIATELY ASKED FOR LOWER AND WAS ASSIGNED 3000 FT. INBOUND IN THE HOLD; JUST PRIOR TO REACHING THE VOR; APCH ADVISED US THAT A CITATION WAS INBOUND ON ANOTHER APCH. THEY THEN ASKED US WHETHER WE WERE ABLE TO DO ONE MORE TURN IN HOLDING. UNSURE WHETHER ICE WAS STILL ACCUMULATING; MY STUDENT AND I DECIDED THAT WE WOULD NOT BE ABLE TO DO SO. WE INFORMED APCH THAT WE WERE INBOUND ON THE APCH; AND THAT WE WERE DECLARING AN EMER. OUR INTENT WAS TO GET OUT OF ICING CONDITIONS AS SOON AS POSSIBLE. PASSING THROUGH ABOUT 2500 FT WE NOTICED THAT WE WERE ABOVE FREEZING AGAIN AND THAT THE ICE WAS DEFINITELY SHEDDING. THE CITATION FIGURED OUT WHAT WAS GOING ON; AND CANCELED HIS IFR AS SOON AS HE WAS VISUAL. CEILINGS WERE ABOUT 900 FT. BY THE TIME WE LANDED MOST OF THE ICE HAD SHED. AFTER RETURNING TO WICHITA; LATER THAT EVENING; WE WERE ASKED TO CALL THE CTL TWR. THE CTLR SAID THAT WE HAD PUT HER IN A VERY DIFFICULT SPOT; AND SHE WOULD APPRECIATE MORE ADVANCED NOTICE WHEN UNABLE TO REMAIN IN A HOLD DUE TO ICING. FROM COMMON KNOWLEDGE I DID NOT TRY TO 'ARGUE' WITH HER BUT SAID THAT I APOLOGIZED FOR THE OCCURRENCE AND WOULD TRY TO BE MORE ACCOMMODATING IN THE FUTURE. I STILL THINK THAT WE DID THE RIGHT THING BY CONTINUING THE APCH. ANYTIME ANY AIRPLANE THAT DOES NOT HAVE DEICE/ANTI-ICE PROTECTION STARTS TO ACCUMULATE ICE; PRIORITY ONE IS TO LEAVE THE ICING ENVIRONMENT. THE ICE WE ENCOUNTERED BUILT SO RAPIDLY THAT WE WERE UNABLE TO CLB; AND THE ONLY OTHER OPTION WAS TO CONTINUE THE APCH.