SMA ON IFR TRAINING FLT ENCOUNTERS ICE AT 12000 FT; LOSES STATIC INSTS AND REQUESTS LOWER ALT. WHEN FINALLY CLRED TO 11000 FT; DSCNT IS BEGUN. DURING DSCNT; ALT STATIC SOURCE IS SELECTED AND INDICATED ALT CHANGED TO 10400 FT. RATHER THAN EXPLAIN; RPTR TOLD ATC HE THOUGHT THEY WERE CLRED TO 10000 FT.

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DURING LONG IFR XCOUNTRY TRAINING FLT; MYSELF AND STUDENT WERE ON AN IFR FLT PLAN IN IMC CONDITIONS NEAR RENO AT 12000 FT WHEN OUR ACFT ENCOUNTERED LIGHT MIXED ICE. I REQUESTED A LOWER ALT. CTR ADVISED THAT NO CHANGE (TO LOWER) COULD BE APPROVED FOR 5 MINS DUE TO OVERTAKING TFC AT LOWER ALT. DURING THE WAIT WE LOST OUR AIRSPD INDICATOR (PITOT HEAT WAS ON). I INFORMED CTR OF THE SIT AND BECAME ADAMANT IN MY REQUEST FOR A LOWER ALT. CTR ADVISED (ISSUED) A DSCNT FROM 12000 FT TO 11000 FT. THE STUDENT BEGAN A HASTY DSCNT; DUE TO THE ICE SIT. DURING THIS TIME THE STATIC SYS BEGAN TO FAIL. I INSTRUCTED THE STUDENT TO SELECT ALTERNATE AIR; WHICH HE DID AND THE STATIC SYS WAS RESTORED. AT THAT POINT WE REALIZED THAT THE INDICATED ALT WAS 10400 FT. AFTER WE ARRESTED THE DSCNT; CTR ASKED OUR ALT; I REPLIED 10400 FT. I MISTAKENLY RPTED THAT I UNDERSTOOD THE ASSIGNMENT AS 10000 FT. DUE TO THE TENSE SIT I; (IN WANT OF AN EXCUSE) WRONGLY STATED THIS; KNOWING THAT THE ASSIGNMENT WAS 11000 FT WITH THE 5 MIN WAIT; AND PITOT STATIC PROB. WE DSNDED THROUGH OUR ASSIGNED ALT. THE ICE WAS LIGHT. WE HAD CHKED FOR PIREPS ON ICE. WE WERE CERTAIN THAT OUR TRIP WOULD KEEP US OUT OF THE ICE. WE DIVERTED TO RENO AS A PRECAUTION AND STAYED THE NIGHT TO CONTINUE OUR TRIP THE FOLLOWING DAY. DURING THE TRIP WE INTENDED RENO AS A DIVERSION IN THE EVENT OF INADVERTENT ICE ENCOUNTERS.