BE10 PLT DECLARES EMERGENCY WHEN COCKPIT FILLS WITH SMOKE. MAY HAVE FAILED TO LEVEL AT CLRED ALT.

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WHILE REPOSITIONING ACFT TO ZZZ AND DSNDING FROM 17000 FT MSL IN IMC AND MODERATE RIME ICING CONDITIONS; WITH ALL ANTI-ICING EQUIP SELECTED ON; I EXPERIENCED SMOKE IN THE COCKPIT WHILE PASSING THROUGH APPROX 10000 FT. WHEN I CHANGED FREQS TO APCH; AS REQUESTED BY CTR; BUT BEFORE CHKING IN; I FIRST SMELLED AND THEN OBSERVED SMOKE COMING FROM BEHIND THE INST PANEL DIRECTLY IN FRONT OF ME. I BELIEVE THAT I WAS CLRED TO DSND TO 9000 FT; ALTHOUGH IT MAY HAVE BEEN 7000 FT; BUT IN ALL THE ENSUING CONFUSION; TRYING TO COMMUNICATE MY EMER TO ATC; RESPONDING TO THEIR REQUESTS; HAND FLY THE ACFT; WHILE TRYING TO DETERMINE AND ISOLATE THE SOURCE OF THE PROB; I MAY HAVE DSNDED THROUGH THE ALT THAT I WAS PREVIOUSLY CLRED TO DSND TO. AS PREVIOUSLY STATED; I AM UNSURE AS TO WHETHER I WAS PREVIOUSLY CLRED TO 9000 FT OR 7000 FT. AT AROUND 7800 FT; I MANAGED TO STOP THE SMOKE BY TURNING OFF THE ENVIRONMENTAL CTL SWITCH AND THE WINDSHIELD HEAT. AFTER COLLECTING MY WITS; I QUERIED ATC AND ASKED THEM WHAT ALT THEY WANTED ME AT. THEY RESPONDED BY AUTHORIZING ME TO DSND TO 4000 FT. THEY DID NOT INDICATE THAT I HAD BUSTED MY ALT OR VIOLATED MY CLRNC IN ANY WAY; BUT I BELIEVE THAT IN ALL THE CONFUSION I MAY HAVE; AS I CANNOT REMEMBER WHETHER I HAD BEEN PREVIOUSLY CLRED TO 9000 FT OR 7000 FT. I CONTINUED TO MY DEST AND LANDED WITHOUT INCIDENT; SOMEWHAT SHAKEN BUT NEVERTHELESS RELIEVED TO BE SAFELY ON THE GND. I DO NOT HAVE ANY SUGGESTIONS AS TO HOW TO PREVENT THIS POTENTIAL INCIDENT FROM RECURRING; BUT ALT PRESELECT EQUIP WOULD HAVE BEEN A NICE ADDITION TO THIS ACFT. THINKING BACK; I SERIOUSLY DOUBT THAT BEING ASKED FOR 'NUMBER OF SOULS ON BOARD AND FUEL REMAINING' DID ANYTHING TO HELP ME DEAL WITH THE EMER; BUT RATHER ONLY SERVED TO DISTRACT ME FROM THE TASK AT HAND AND INCREASED MY CONCERN ABOUT MY PREDICAMENT; SHOULD THAT BE POSSIBLE. REGARDLESS; ASKING THIS INFO IS REDUNDANT AT BEST; AS IT IS ALREADY ON THE FLT PLAN. IT CERTAINLY HAD NO BEARING ON MY SITUATION AND DID NOTHING TO HELP ME RESOLVE THE PROB. AT BEST; IT ONLY SERVED TO CONTRIBUTE TO THE CONFUSION AND PROVIDED AN UNNECESSARY DISTR. I BELIEVE THAT REQUIRING THIS INFO; WHEN INDICATED ON FLT PLAN; IS A WASTE AND ADDS CONFUSION.