WX FACTORS - ACR ENCOUNTERS SEVERE ICING IN UNPRESSURIZED FLT WITH UNDER-PWRED ENGS.

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WE DEPARTED LANSING AND WERE CLRED TO OUR FINAL ALT OF 8000 FT. USUALLY WE FLY AT 12000 FT ON THIS LEG; BUT THE PRESSURIZATION SYS HAD BEEN DEFERRED. ON THE FLT INTO LANSING; WE FOUND THE TOPS TO BE AT 6500 FT AND THE BASES AT 2500 FT; SO WE EXPECTED TO BE ON TOP AT 8000 FT. DURING THE CLB WE ENCOUNTERED A TRACE OF RIME ICE; JUST AS WE HAD IN THE DSCNT. WE LEVELED OFF AT 8000 FT; ON TOP AND CLR ABOVE. AFTER A FEW MI; HOWEVER; THE TOPS ROSE TO MEET US; AND WE BEGAN EXPERIENCING LIGHT CHOP AND LIGHT TO MODERATE ICING. WE CALLED KALAMAZOO APCH AND REQUESTED 9000 FT. APCH SAID THEY HAD TO CLR IT WITH CTR AND TO STANDBY. AFTER SEVERAL SECONDS THEY TOLD US TO CALL CTR; THAT THEY HAD OUR REQUEST. WE CONTACTED CTR AND WERE TOLD TO REMAIN AT 8000 FT; THAT HE COULD HAVE 9000 FT FOR US IN 'JUST A MOMENT.' NOW WE NOTED OUR AIRSPD BEGINNING TO DROP; AND WE INFLATED THE WING AND TAIL BOOTS; AS THE ICE WAS NOW 1/2-1 INCH THICK. THE BOOTS INFLATED; BUT DID NOT SHED ALL THE ICE; AND THERE SEEMED TO BE NO EFFECT ON OUR DECREASING AIRSPD. AT THIS POINT WE BECAME CONCERNED; REALLY CONCERNED; AND THE DECISION WAS MADE TO DECLARE OUR EMER AUTH TO CLB. RIGHT AS WE INITIATED THE CLB; CTR CLRED US TO 9000 FT. AIRSPD IN LEVEL FLT HAD DROPPED FROM 220 KIAS TO 170-180 KIAS; AND IN THE CLB WE SLOWED TO 140 KIAS. AT ABOUT 8700 FT; THE ACFT BEGAN TO SHAKE WILDLY; AND I IMMEDIATELY LOWERED THE NOSE FEARING AN IMMINENT STALL. THE AIRSPD ROSE; AND AS THE VIBRATION DID NOT ABATE; WE DETERMINED IT WAS DUE TO EXCESSIVE AND ASYMMETRICAL ICE ACCUMULATION ON THE PROPS. I HAD FLOWN SCHEDULED RTES IN THE GREAT LAKES AREA FOR 2 WINTERS; AND HAD FELT PROP ICE BEFORE; BUT NOT LIKE THIS. WE CONTINUED THE CLB AT 140 KIAS; AND WE NOTED THE CLB RATE DETERIORATING. WE ADVANCED THE SPDS TO HIGH. WE REACHED 9000 FT; BUT WERE STILL IN CLOUD. NEVER SLOWING THE CLB; WE ASKED FOR AND RECEIVED A BLOCK; 9000-10000 FT. WE BROKE OUT ON TOP AT ABOUT 9300 FT; CLR ABOVE. THE VIBRATION CONTINUED; AND IT WAS ONLY THROUGH CHANGING PWR SETTINGS; SPD SETTINGS AND PORPOISING THE ACFT TO CHANGE THE PROP PARAMETERS THAT THE ICE WAS FINALLY SHED - LARGE CHUNKS THAT SLAMMED INTO THE FUSELAGE LIKE A SHOTGUN RPT. PAX AFTER LNDG STATED THEY COULD SEE THE CHUNKS FLASH BY THE WINDOWS. WE RPTED SEVERE ICING TO ZAU AND CONTINUED AT OUR BLOCK ALT FOR ANOTHER 20-30 MI; UNTIL CTR GAVE US A DSCNT TO 5000 FT; UNDER THAT AREA'S BASES. THERE WAS NO FURTHER INCIDENT INTO CHICAGO. THERE WERE 2 SIGNIFICANT THINGS THAT I LEARNED FROM THIS EXPERIENCE. FIRST AND FOREMOST IS SOMETHING I HAVEN'T YET MENTIONED. WHEN WE WERE CLBING OUT OF LANSING; WE NOTED THAT THE PWR LEVERS WERE FIREWALLED; YET NEITHER THE TORQUE LIMIT NOR THE EGT LIMITS HAD BEEN REACHED. THE ENGS HAD BEEN RIGGED WRONG; AND THE FULL PWR OF THE ENGS AT THAT ALT WAS NOT AVAILABLE. WE HAD FULL PWR AT SEA LEVEL. THE ENGS MADE TARGET TORQUE AND EVERYTHING APPEARED NORMAL; BUT AT ALT WE WERE UNDER-PWRED. SEEMINGLY UNRELATED TO THIS SIT WAS THE FACT THAT WE WERE UNPRESSURIZED (THE DOOR SEAL HAD BEEN SQUEALING THAT DAY; AND MAINT HAD DISABLED THE PRESSURIZATION FOR THE MEL). THESE 2 FACTORS; HARMLESS THOUGH THEY MAY SEEM IN NORMAL OPERATING CONDITIONS; BECAME DANGEROUS AND INSIDIOUS; WHEN WE WERE FACED WITH SEVERE ICE; OUR ALTS WERE RESTRICTED (OUR ORIGINAL ALT OF 12000 FT WOULD HAVE CARRIED US TO CHICAGO WITHOUT INCIDENT); AND OUR PWR WAS LIMITED (IT HELPS TO HAVE FULL PWR AVAILABLE WHEN TRYING TO CLB WITH A LOAD OF ICE). IT'S A LOT BETTER TO START THE DAY WITH A CLEAN SLATE. SECONDLY; I LEARNED FIRSTHAND HOW UNPREDICTABLE ICING IS AND HOW LOCALIZED SEVERE ICING CAN BE. WHEN DSNDING INTO LANSING AND THEN DURING CLBOUT; WE ACCUMULATED ONLY A TRACE OF RIME ICE; OVER AN AREA OF 15-20 MI. YET A FEW MILES AWAY; THE ICE ACCUMULATED SO QUICKLY THAT NEITHER THE PROP HEAT NOR THE DEICING BOOTS COULD KEEP UP. IN THE FUTURE I'LL BE A LOT QUICKER TO AVOID 'LIGHT TO MODERATE ICE;' BECAUSE I REALIZE HOW FAST IT MAY CHANGE FOR THE WORSE.