FLC OF AN MLG LOST ALL NORMAL COMS WITH ATC AND SUBSEQUENTLY RECEIVED VECTORS ON EMER FREQ FOR AN APCH IN IMC.

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LOST COM. APPARENT RADIO FAILURE. APCH CTL ADVISED MY FLT TIED UP APCH CTL FREQ 118.95 UNTIL LNDG; EVEN WITH OTHER FREQS SELECTED. BEFORE LEAVING LAN WE HAD A 'HDG' INST ANNUNCIATOR LIGHT WHICH WENT OUT AT ENG START. SUSPECTED A PHASE PROB WITH APU GENERATOR (THIS POSSIBILITY LATER HELPED CONFUSE THE PROB SOLVING). HALFWAY TO DTW WE ENCOUNTERED MODERATE RIME ICE WITH ALL THE ATTENDANT NOISE; THE RADIOS BEGAN TO HISS AND CRACKLE (LIKE WHEN THE VHF ANTENNA ICES UP). AFTER ABOUT 5-7 MINS OF SILENCE ON THE RADIO (AT XA00 THERE ISN'T MUCH CHATTER ANYWAY) WE ATTEMPTED CONTACT SINCE WE FELT WE WERE WELL WITHIN COMMENCEMENT OF DSCNT RANGE FROM DTW. NO ANSWER. WE TRIED SEVERAL OTHER APCH CTL FREQS AND FINALLY GOT INTERMITTENT CONTACT ON 121.5. WE WERE VECTORED AROUND FOR A RWY 31R ILS; BROKE OUT AT ABOUT 3000 FT MSL AND LANDED. COULDN'T EVEN TALK TO GND CTL AFTER LNDG. SINCE IT WASN'T BUSY YET WE TAXIED ON IN TO THE GATE (WE ESTABLISHED CONTACT WITH COMPANY RAMP CTL WITH NO PROB). COM PROB ENTERED INTO MAINT LOG. I HAVE NOT YET FOUND OUT THE PRECISE NATURE OF THE RADIO FAILURE. IN SPITE OF THE UNGODLY HOUR; A SHORT UNCOMFORTABLE LAYOVER; DARKNESS AND WX (MODERATE ICING) I FELT WE ANALYZED THE PROB WELL ENOUGH TO ESTABLISH SUFFICIENT COMS TO LAND. IT WAS LONG BEFORE ANY BUSY TIME AT DTW SO OTHER TFC WAS NOT A PROB AND WE WERE ABLE TO DEAL WITH THE RADIO FAILURE IN AN UNPRESSURED; ALMOST LEISURELY FASHION; WITHOUT ALARMING OUR PAX. EVEN LANDED ON SCHEDULE. WHEN I PHONED APCH CTL; THE SUPVR WASN'T CONCERNED OR ALARMED.