Narrative:

I was flying on a scheduled freight route. A snow storm had entered the area and was across the entire route. Upon leaving; I entered IMC almost immediately and was IMC during the entire flight. The temperatures were -1 C entering IMC and -10 C at 8;000 ft. I immediately started to pick up ice after leaving. About 30 miles into the flight I entered an area of moderate ice and went up to 8;000 to try and slow the progression. It helped but I still continued to get light ice with small pockets of moderate. All the deice equipment on the airplane was operational but the ice continued to form on the parts of the airplane not equipped with deice equipment. As a rule of thumb; if the airplane airspeed falls below 150; the pilot needs to take evasive action to get out of it. I was actually down to 140 KTS in level flight but I was close enough to destination that I needed to start a descent to get set up for the approach. I was 40 miles out when I got the weather and it was 1 1/4 miles and 600 ft overcast; shortly after that center advised me that the weather was going down. At this point; I had already started my descent and was maintaining 140 KTS. I had started to run out of options at this point because the airplane had picked up enough ice I did not think I would be able to climb back up. I was maintaining airspeed only because I was descending. The visibility had dropped to 1/4. I elected to do the ILS approach rather than hold due to the ice the airplane had already encountered. I landed without incident with the actual visibility almost one mile. The trucks were plowing the runway and the wind was blowing in the right direction so that the snow off the runway was moving over the sensor. The snowstorm was the actual cause of the problem and the inaccurate taf. While the weather was supposed to come down it was not supposed to drop below 1 1/2 according to the taf. I was fully aware of the snowstorm and possible icing condition but also had many options for most of the flight.

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Original NASA ASRS Text

Title: A PA31 pilot departed on a one hour flight into icing conditions with forecast snow and low visibilities at destination. Ice formed on areas of the aircraft that are not deiced and airspeed dropped. Descent was required to maintain airspeed and an ILS approach and landing was made with visibility reported as one quarter mile.

Narrative: I was flying on a scheduled freight route. A snow storm had entered the area and was across the entire route. Upon leaving; I entered IMC almost immediately and was IMC during the entire flight. The temperatures were -1 C entering IMC and -10 C at 8;000 FT. I immediately started to pick up ice after leaving. About 30 miles into the flight I entered an area of moderate ice and went up to 8;000 to try and slow the progression. It helped but I still continued to get light ice with small pockets of moderate. All the deice equipment on the airplane was operational but the ice continued to form on the parts of the airplane not equipped with deice equipment. As a rule of thumb; if the airplane airspeed falls below 150; the pilot needs to take evasive action to get out of it. I was actually down to 140 KTS in level flight but I was close enough to destination that I needed to start a descent to get set up for the approach. I was 40 miles out when I got the weather and it was 1 1/4 miles and 600 FT overcast; shortly after that Center advised me that the weather was going down. At this point; I had already started my descent and was maintaining 140 KTS. I had started to run out of options at this point because the airplane had picked up enough ice I did not think I would be able to climb back up. I was maintaining airspeed only because I was descending. The visibility had dropped to 1/4. I elected to do the ILS approach rather than hold due to the ice the airplane had already encountered. I landed without incident with the actual visibility almost one mile. The trucks were plowing the runway and the wind was blowing in the right direction so that the snow off the runway was moving over the sensor. The snowstorm was the actual cause of the problem and the inaccurate TAF. While the weather was supposed to come down it was not supposed to drop below 1 1/2 according to the TAF. I was fully aware of the snowstorm and possible icing condition but also had many options for most of the flight.

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.