C210N ENCOUNTERED AIRFRAME ICING. RPTR MADE SOME POOR CHOICES OF ALTS AND THE SIT BECAME SERIOUS. THE RPTR COULD NOT MAKE UP HIS MIND WHETHER OR NOT TO DIVERT TO JST SO ATC MADE THE CHOICE FOR HIM AND VECTORED HIM TO THE ARPT.

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I WAS ENRTE FROM N67 TO CMI. I WAS IMC AT 6000 FT WITH NO ICE INITIALLY. AT ALTOONA I BROKE OUT INTO A CLR AREA WITH NO CLOUDS ABOVE. A RECENT RPT SAID TOPS WERE 11000 FT. I CONSIDERED ASKING CTR FOR 12000 FT ALTHOUGH THE WINDS AGAINST ME WOULD HAVE BEEN HIGHER. UNFORTUNATELY I ABANDONED THAT GOOD IDEA AND OPTED TO STAY AT 6000 FT WHERE; IT APPEARED I WOULD BE BTWN LAYERS AND MAKE BETTER TIME. A FEW MI FROM JOHNSTOWN THIS OPEN AREA CLOSED AND I BEGAN PICKING UP CLR ICE QUITE RAPIDLY. I ASKED ZOB FOR VECTORS TO AN APCH AT JST. THEY RPTED THE CONDITIONS THERE WERE 300 FT OVCST AND 3 MI. I WAS NOT SURE I WOULD SHED ANY ICE THERE ON MY WAY TO MINIMUMS AND IT APPEARED THAT I MIGHT BE IN REAL TROUBLE BEFORE I COULD GET LINED UP FOR THE ILS. PART OF ME WANTED TO RETURN TO ALTOONA (A LONG WAY BACK). CTR GAVE ME THE OPTION OF GOING ON TO LATROBE (20 MINS) I WAS HAVING A TOUGH TIME MAKING A DECISION AND SPENDING TOO MUCH TIME CONCENTRATING ON THE BUILDING ICE. CLEVELAND MADE THE CHOICE FOR ME BY GIVING VECTORS FOR A SHORT DOWNWIND TO JOIN THE ILS RWY 33 AT JST. I WENT BELOW THE APCH ALT OF 4600-(4000 FT) IN MY UNCONSCIOUS DESIRE TO PERHAPS MELT SOME OF THE BUILDING ICE. CTR GAVE ME THE ILS FREQ AND I FINALLY CALMED DOWN ENOUGH TO USE THE AUTOPLT TO GET OUT THE APCH PLATE. I BEGAN TO LOSE SOME ICE ON FINAL AT ABOUT 2900 FT AND LANDED WITHOUT FURTHER INCIDENT. I'M INDEBTED TO THE CALM DECISIVENESS OF THE ZOB CTLR HANDLING ME. THIS WAS THE MOST ICE I HAD EXPERIENCED AND THE FIRST CLR ICE. IN RETROSPECT I SHOULD HAVE: TAKEN THE FIRST OPTION TO STAY OUT OF TROUBLE -- (CLR SPACE AT ALTOONA TO TOP THE OVCST); DONE AN IMMEDIATE 180 DEGS WHEN ENCOUNTERING THE FIRST ICE; USED THE AUTOPLT TO GET ORGANIZED FOR THE APCH AND CONCENTRATED ON FLYING THE AIRPLANE INSTEAD OF CONCENTRATING ON THE ICE WHICH ONLY INTENSIFIED MY GROWING PANIC. (AT THAT POINT THERE WAS NOTHING I COULD DO ABOUT THE ICE AND THE FASTEST WAY OUT OF THE MESS WAS TO SHOOT A FLAWLESS APCH TO MINIMUMS) I DID USE THE ANTI- ICE EQUIP AVAILABLE TO ME -- PROP BOOTS; PITOT HEAT AND WINDSHIELD DEFROSTER. I HAVE NO EXCUSE FOR THE SECOND ALT EXCURSION EXCEPT MY NERVOUSNESS ABOUT ICE THAT HAD BEEN RPTED AS NON-EXISTENT BY THE MALIBU. I ALSO NOW HAD THE OPTION OF DSNDING TO A MUCH LOWER ALT AT LATROBE IF NECESSARY. (THE ACFT WAS CLR OF ICE AT THE TIME.)