20120905023859I

Era 874, dash 8, departed ted stevens international airport, Anchorage, AK on a scheduled flight to homer, AK with 12 passengers and three crewmembers. The flight was the second mission on that day for the flight crew. Initial clearance altitude was 10,000' MSL along a normal route of flight. The crew stated they received a verbal update on weather and notices to airman from their dispatch prior to departing the gate area indicating no significant changes along their route of flight and destination. The crew stated they received no additional pilot reports or weather warnings while taxiing for departure or after they departed.ATC audio recordings show a general icing announcement from another aircraft along the intended route of flight. En route to homer, passing through 8,000' MSL, the crew encountered weather and activated all aircraft anti-ice equipment. Aircraft anti-ice equipment operated normally. Leveling off at 10,000' MSL, the crew encountered icing conditions. The crew requested and received a block altitude of 10,000' MSL - 14,000' MSL in order to depart the icing conditions. The crew informed anc ATC the icing was moderate mixed icing with an outside air temperature of -9C.during the climb, the crew noticed increased icing on the aircraft at an elevated level. The crew characterized the icing onset as the deice boots would shed ice and then ice would immediately build back up. The pilot stated icing formed farther aft than normal on the propeller spinner on the left engine, approximately 6" back. This is a visual cue described in AD 96-09-25, which then requires immediate disengagement of the autopilot and was not accomplished by the PIC.the aircraft anti-ice equipment appeared to be shedding the ice as expected. Passing approximately 11,400' MSL, the crew stated they began to see clearing skies and elected to level off at 12,000' MSL to continue to their destination. As they were leveling off, the aircraft shuttered as if ice on the propellers was being shedded, a normal sensation for the aircraft. However, the shuttering intensified and the aircraft rolled to the left and began a uncommanded descent. The crew disconnected the autopilot and attempted to recover the aircraft. Both crewmembers stated they did not recall the stick shaker activating. The pilot stated he attempted several times to recover the aircraft without initial success. He stated nothing he did seemed to be working. Sometime during the descent, the aircraft responded to the pilot flight control inputs and began to recover. At no time did the pilot transfer aircraft control to the first officer to determine in the pilot flight controls were inoperative. The first officer stated that he wanted to take over the flight controls but felt his position was as pilot monitoring. The aircraft was recovered at 7,000' MSL on a westerly heading. The crew declared an emergency and requested a descent to 5,000' MSL with a clearance back to Anchorage, AK.ATC center R5 position response to the flight crew declaration of the emergency. The center clearance was without increased concern or question. R5 appeared to either not understand the emergency declaration or missed the emergency call. Controller R5 continues to vector era 874 back to Anchorage without inquiring about the nature of their return or that they were cleared to 10,000 MSL initially and then a block altitude of 10,000 - 14,000' MSL but reported back on at 6,000' MSL.the aircraft was recovered uneventfully back to ted stevens international airport. There were no injuries. The aircraft was impounded for an airworthiness inspection. The flight crew was current and qualified for their positions.