A C208B pilot reported flying into unforecast icing at 7;000 FT which the aircraft's de-ice could not clear from the wings. Unable to control aircraft's descent; he diverted to a nearby airport and landed safely.

Narrative

This is a report as to why the flight diverted. I was the pilot in command and had 1400 LBS of fuel on board. At XA:20 I checked the weather report via website for a standard briefing along my route of flight. The route to my final destination with one enroute stop. At XB:20 I called 800-WX-BRIEF to get a briefing on icing conditions and any hazardous weather along my route of flight. The briefer stated that there was light rime ice from a pilot report. I asked him if there were any other reports along the said route; and no reports were issued. At XB:45 I checked the weather via website again for any adverse weather; icing conditions and PIREPS. At this time there were no reports of any ice along the route of flight. At XC:15 I called Dispatch to let them know I was on duty. At XC:26 the courier arrived at the airport and dropped off 31 LBS of freight. At XC:32 I lifted off en route with stall heat and pitot heat on. On climb out passing through the first layer of clouds (1100 FT AGL); I reported to Center light rime ice was observed. After cruising flight at 7000 FT MSL I was between layers of clouds but would be entering IMC soon. I turned on the windshield anti-ice; prop anti-ice as well as putting out the inertial separator and turning on the ignition. I entered the clouds very quickly and reported to Center I was picking up moderate clear ice. I made use of the boots on the C-208 to break off the clear ice. After just 5 minutes I had asked Center for a higher altitude. I was told to maintain a block altitude from 7000 FT MSL to 11000 FT MSL. I started my climb but noticed the aircraft would only climb 200 FPM at 120 KTS. I reached 7500 FT MSL and could no longer climb. The aircraft could hold altitude at maximum power and 120 KIAS for a short time. After approximately 10 minutes the aircraft started to buffet at 120 KIAS and I reported severe clear ice. I pitched the aircraft nose down to keep from a stall. I notified Center that I would not be able to maintain my block altitude assignment and would need lower. I was given a block from 4500 FT MSL to 7000 FT MSL. As time progressed I continued using the boots on the airplane as well as trying to find VFR weather conditions. At 4000 FT MSL I had declared an emergency with Center; as I would no longer be able to hold altitude. The aircraft at this time was at maximum power and stalling at 120 KIAS. I was diverted to the closest airport to shoot the VOR DME approach. After Center had told me I had to cross the VOR at 4000 FT MSL; I replied I couldn't maintain altitude and I would not make it to my divert airport. I was told from my last known heading there was a small airport at 3 o'clock and 5 miles. I broke out of the clouds at 500 FT AGL and quickly started a steep turn to look for a field to land in; only being able to view from where the hot plate was. Center picked me up again and told me the airport was 1 o'clock and 4 miles. I asked Center for the frequency to turn on the landing lights. At this time another pilot flying out of the conditions turned the lights on for me. I would not make it to the north and south runway. I again had full power to maintain 125 KIAS and a 200 FPM descent. I landed on a closed runway after stalling the aircraft 10 FT above the field with maximum power at 120 KIAS and applied maximum braking and maximum reverse to stop the airplane. I contacted Center on the ground to inform them I had landed safely. After I had shut down the aircraft I then called Dispatch to let them know of the situation and then contacted the Assistant Chief Pilot. After I had notified the correct people; I went outside to asses the damage; to find there was none to the aircraft or myself.