FLC OF A BEECH 1900 AIRLINER (BE02) FAILED TO MAINTAIN ASSIGNED ALT WHEN ENCOUNTERING UNFORECASTED SEVERE ICING CONDITIONS AND FREQ CONGESTION PREVENTED THEM FROM OBTAINING IMMEDIATE DSCNT APPROVAL FROM ATC. AS THEY DSNDED ATC FINALLY REPLIED TO THEIR EMER AND PROVIDED A VECTOR HDG TO AVOID OTHER TFC.

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OUR FLT WAS CLBING TO 15000 FT MSL AFTER TKOF FROM UES. ENRTE TO LUK; WE BEGAN PICKING UP MODERATE ICE AT 7600 FT MSL. ICE ACCUMULATION CONTINUED THROUGH 11000 FT IN THE CLB. WE REQUESTED DSCNT TO 9000 FT FOR ICE AND WERE APPROVED. AFTER A SHORT TIME AT 9000 FT; THE SIT BEGAN TO WORSEN. THE ACFT DEICE ANTI-ICE SYS WERE FUNCTIONING PROPERLY; BUT BECAUSE OF 'NON SHEDABLE' ICE ON THE AIRFRAME; WE BEGAN LOSING AIRSPD AT THE RATE OF APPROX 1 KT EVERY 10 SECONDS. BECAUSE OF VERY HVY TFC ON THE FREQ WE WERE UNABLE TO CONTACT THE CTLR TO REQUEST LOWER ALT RIGHT AWAY. AFTER APPROX 90 SECONDS WE GOT AN OPENING ON THE FREQ AND REQUESTED AN IMMEDIATE DSCNT TO 7000 FT BECAUSE OF ICING. THERE WAS NO REPLY. AIRSPD NOW AT 160 KTS; DOWN FROM 200 KIAS; I FORCEFULLY XMITTED THAT WE WERE 'VACATING 9000 FT FOR 7000 FT BECAUSE OF HVY ICING.' THE CTLR RESPONDED; 'WELL; IF YOU'RE GOING TO DO THAT; TURN R TO 220 DEGS; YOU HAVE TFC AT 11 O'CLOCK AT 8 MI AT 8000 FT.' PROB: EXTREMELY HVY RADIO FREQ TFC HAMPERING EFFECTIVE AIR-TO-GND COM; INDIFFERENT ATTITUDE OF CTLR. ZAU FREQ NOT RECORDED.