AN M20P PLT CAUGHT BY THE WX AND UNABLE TO CONTACT TWR DUE TO A FAULTY RADIO; LANDED AT TTD; A CLASS D ARPT; WITHOUT A CLRNC.

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WE WERE AT +/-15 MI E OF DLS AT 4500 FT. PROCEEDED DOWN COLUMBIA GORGE EXPECTING TO GET TO SPB WITH 1W1 (CARNAS) AND TTD AS ALTERNATES. SHOWERS BEGAN AT BONNEVILLE DAM WITH LOWERING CEILINGS; SO DROPPED DOWN TO 600 FT AGL AFTER XING PWR LINES AT DAM. PROCEEDED DOWN RIVER IN CLASS G AIRSPACE; CLR OF CLOUDS; RIVER IN SIGHT CLRLY; BOUNDARY MOUNTAINS OBSCURE. (THOUGHT I WAS IN CLASS G CONDITIONS WITH ELECTRICITY OUTAGE NEAR TTD.) NEARING TTD CLASS D AIRSPACE; VISIBILITY IMPROVED; BUT HILL TOPS OBSCURED SO UNABLE TO SKIRT CLASS D AIRSPACE. CALLED TWR TWICE BUT NO ANSWER. DID NOT THINK IT SAFE TO DO '180' BECAUSE OF LACK OF GOOD VISIBILITY; ESPECIALLY BACK UP RIVER WITH POSSIBLE OBSCURATION OF PWR LINES AT BONNEVILLE. ABLE TO CLRLY SEE STEAM FROM MILL OPPOSITE TTD ON WASHINGTON SIDE; SO CONTINUED INTO CLASS D AIRSPACE. NO LIGHTS VISIBLE ON OREGON (S SIDE) SIDE NEAR TTD. OVER RIVER; DECIDED IT TO BE TOO HAZARDOUS TO ATTEMPT XING HILLS TO N TO GET TO 1W1 (CARNAS) ONLY 3 OR 4 MI AWAY. CALLED TWR AGAIN AS BUILDING (HOTEL) CAME IN SIGHT (NEAR AND AT TTD RWY; NO LIGHTS VISIBLE). DECIDED TO CONTINUE ON EXTENDED R BASE. CALLED TWR -- NO RESPONSE. FOCUSED ON OPPORTUNITY TO LAND AND POSSIBLE OTHER ACFT IN PATTERN. COULDN'T SEE TWR (NO LIGHTS). LANDED AS NO MOVEMENT ON RWY; IN PATTERN; OR TXWYS. TURNING OFF RWY; I LOOKED UP; SAW LIGHTS IN TWR; CYCLED #2 COM; BANGED IT AND TALKED TO TWR. #2 COM NOW IN SHOP.