Narrative:

In cruise; I began accumulating ice. I activated all anti and de-icing systems and monitored the situation by watching the wing leading edge via the wing ice light. Additionally; I was monitoring the OAT probe for accumulation. What I failed to notice initially was the ice building aft of the boot. Once I noticed; I requested an immediate climb; thinking that perhaps I was encountering freezing precipitation and/or sld. In the climb; the airspeed decayed to the point where I determined that my only option was to level off and build up some speed for the wing deice boots (and for minimum icing speed considerations) and failing that; I would have to descend and potentially divert. I leveled at an intermediate altitude for several minutes while I activated the deice boots. The airframe cleared of much of the ice and I was able to climb to my assigned altitude. I informed ATC of the reason for stopping my climb and that I was continuing to climb to 8;000 ft. The controller seemed disinterested; so I felt that there was no potential loss of separation. I continued and landed at the destination. On the approach; the stall warning device activated at approximately 125 KTS; though physical cues (I was hand-flying) of an impending stall were absent. I was able to land without incident. When I inspected the aircraft after landing there was as much as 1-1/2' of ice on certain unprotected parts and approximately 3/4' on the stall warning device. I should have monitored the area aft of the boots when I began accumulating ice. I believe that the ice accumulating on unprotected surfaces caused my climb airspeed to be too low and that caused the intermediate level-off. From now on; I will monitor unprotected surfaces.

Related reports:

Google
 

Original NASA ASRS Text

Title: A PA31 encountered icing conditions that the aircraft deice systems initially were unable to handle. After leveling off; much of the ice successfully shed and a climb to 8;000 FT and slower ice accumulation was made.

Narrative: In cruise; I began accumulating ice. I activated all anti and de-icing systems and monitored the situation by watching the wing leading edge via the wing ice light. Additionally; I was monitoring the OAT probe for accumulation. What I failed to notice initially was the ice building aft of the boot. Once I noticed; I requested an immediate climb; thinking that perhaps I was encountering freezing precipitation and/or SLD. In the climb; the airspeed decayed to the point where I determined that my only option was to level off and build up some speed for the wing deice boots (and for minimum icing speed considerations) and failing that; I would have to descend and potentially divert. I leveled at an intermediate altitude for several minutes while I activated the deice boots. The airframe cleared of much of the ice and I was able to climb to my assigned altitude. I informed ATC of the reason for stopping my climb and that I was continuing to climb to 8;000 FT. The Controller seemed disinterested; so I felt that there was no potential loss of separation. I continued and landed at the destination. On the approach; the stall warning device activated at approximately 125 KTS; though physical cues (I was hand-flying) of an impending stall were absent. I was able to land without incident. When I inspected the aircraft after landing there was as much as 1-1/2' of ice on certain unprotected parts and approximately 3/4' on the stall warning device. I should have monitored the area aft of the boots when I began accumulating ice. I believe that the ice accumulating on unprotected surfaces caused my climb airspeed to be too low and that caused the intermediate level-off. From now on; I will monitor unprotected surfaces.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.