SMA ON IFR FLT PLAN ENCOUNTERS ICING. PITOT SYS CAUSES ERRONEOUS INST INDICATIONS.

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WE LEFT FFO (WRIGHT-PATTERSON AFB) ON AN INST FLT PLAN. WE HAD FILED FOR 8000 FT. IT WAS OUR DESIRE TO GET SOME PRACTICE IN ACTUAL INST CONDITIONS. THEREFORE WE ASKED DATYON APCH FOR CLB TO 10000 FT AND THEY GRANTED OUR REQUEST. UPON DOING SO; AND REMAINING THERE FOR SEVERAL MINS; WE BEGAN TO ENCOUNTER SOME RIME ICE FORMATION. THE QUANTITY OF ICE WOULD HAVE BEEN DESCRIBED AS TRACE. WE NOTICED A SMALL JUMP IN OUR INSTS AND ASSUMED WE HAD HIT AN UPDRAFT. A COUPLE OF MINS LATER WE NOTICED AN INCREASE IN OUR AIRSPD AND A MUCH GREATER (APPROX 800 FT) CHANGE IN OUR INSTS. AT THIS TIME WE REALIZED THAT WE HAD NOT TURNED ON OUR PITOT HEAT. AS SOON AS WE DID THIS; OUR INSTS STABILIZED AND WE CALLED THE CTLR AND ADVISED THEM OF THE SIT. WE BEGAN OUR CLB BACK TO OUR ASSIGNED ALT. WE EXPERIENCED NO PROBS FROM THERE ON. SINCE WE STILL APPEARED TO BE PICKING UP A TRACE OF ICE; WE DSNDED TO 8000 FT TO GET OUT OF THE CLOUDS. I FEEL THE CONTRIBUTING FACTORS IN THIS SIT WERE MY LACK OF EXPERIENCE IN DEALING WITH AN ICING SIT. PERSONAL CORRECTIVE ACTIONS THAT I TOOK UPON RETURNING FROM THIS FLT TO HELP TO INSURE THIS SAME ERROR DOES NOT OCCUR AGAIN WERE MY DISCUSSIONS WITH A CFII AND THE WRIGHT-PATTERSON AFB CHIEF OF FLT SAFETY.