Narrative:

This was my first time flying into the ZZZ area. The ceiling was scattered to broken and it appeared from PIREPS that I would be on top at 11;000 MSL. The temperature was above freezing at the surface. There were large areas of blue sky mixed with areas of cloud. I was flying a standard instrument departure but started to receive vectors which would put me into the clouds. I requested a deviation to stay clear of the clouds because I had noticed that the OAT had dropped below freezing. ATC was unable to approve any immediate deviation due to landing traffic at ZZZ; but said that they would have higher in 5 miles. At this point; I was in and out of the broken layer of cloud and began to accumulate rime ice. I notified ATC; and they authorized a climb from 8;000 feet to 9;000 feet. This did not allow me to get clear of clouds; and the accumulation intensified in the climb. Also; the rate of climb was significantly lower than usual; even at that altitude. At this point; I elected to divert to a nearby airport. Only a very short time elapsed from the time I noticed the first trace of ice until I elected to divert. I began to receive vectors for the ILS. I then put the plane on automatic pilot while I searched for the approach plate. After I intercepted to localizer; I was cleared for the approach. When I turned off the autopilot the vsi showed a steep descent momentarily until I pulled back on the yoke. At this point; I received a low altitude alert. After that; the ice began to melt and I made an uneventful no flap approach and landing. I learned a lot from this experience. First; I learned that I need to improve my weather briefing review and need to anticipate icing any time I am flying in visible moisture. There were some pilot reports of icing; but they weren't in the immediate area of my flight and I was expecting to stay clear of clouds. Second; I cannot count on ATC permitting a climb that will permit me to remain clear of clouds; particularly in a busy terminal area. Third; I saw firsthand the impact of icing on the tail and how its effects are masked by the autopilot. While I was thinking of the effects of the high altitude at ZZZ; I probably underestimated somewhat its effect on the airplane's performance; particularly in icing conditions. This made the prospect of a successful climb on top unlikely. Fourth; I need to be more precise and maintain focus at all times; particularly on headings and altitudes in the terminal area. The icing had become a distraction to precise flying. Finally; I learned that I have to improve my cockpit organization; and should have all conceivably necessary approach plates in arms reach in case I need to divert. While I had read a lot about icing and its effects; I did not anticipate how quickly performance would degrade from such a brief encounter; particularly regarding the tail. There was never more than perhaps 1/4 inch on the wing; but likely more on the tail and that was enough for it to lose some of its effectiveness. I was glad that I diverted immediately and made a relatively uneventful landing; but I will be extra vigilant next time icing is forecast.

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Original NASA ASRS Text

Title: An M20J pilot encounters icing conditions while IFR in a busy terminal area and is unable to obtain a clearance to exit the condition. Must divert to a nearby airport and temporarily loses control when the airplane pitched down aggressively when the autopilot was disconnected.

Narrative: This was my first time flying into the ZZZ area. The ceiling was scattered to broken and it appeared from PIREPS that I would be on top at 11;000 MSL. The temperature was above freezing at the surface. There were large areas of blue sky mixed with areas of cloud. I was flying a Standard Instrument Departure but started to receive vectors which would put me into the clouds. I requested a deviation to stay clear of the clouds because I had noticed that the OAT had dropped below freezing. ATC was unable to approve any immediate deviation due to landing traffic at ZZZ; but said that they would have higher in 5 miles. At this point; I was in and out of the broken layer of cloud and began to accumulate rime ice. I notified ATC; and they authorized a climb from 8;000 feet to 9;000 feet. This did not allow me to get clear of clouds; and the accumulation intensified in the climb. Also; the rate of climb was significantly lower than usual; even at that altitude. At this point; I elected to divert to a nearby airport. Only a very short time elapsed from the time I noticed the first trace of ice until I elected to divert. I began to receive vectors for the ILS. I then put the plane on automatic pilot while I searched for the approach plate. After I intercepted to localizer; I was cleared for the approach. When I turned off the autopilot the VSI showed a steep descent momentarily until I pulled back on the yoke. At this point; I received a low altitude alert. After that; the ice began to melt and I made an uneventful no flap approach and landing. I learned a lot from this experience. First; I learned that I need to improve my weather briefing review and need to anticipate icing any time I am flying in visible moisture. There were some pilot reports of icing; but they weren't in the immediate area of my flight and I was expecting to stay clear of clouds. Second; I cannot count on ATC permitting a climb that will permit me to remain clear of clouds; particularly in a busy terminal area. Third; I saw firsthand the impact of icing on the tail and how its effects are masked by the autopilot. While I was thinking of the effects of the high altitude at ZZZ; I probably underestimated somewhat its effect on the airplane's performance; particularly in icing conditions. This made the prospect of a successful climb on top unlikely. Fourth; I need to be more precise and maintain focus at all times; particularly on headings and altitudes in the terminal area. The icing had become a distraction to precise flying. Finally; I learned that I have to improve my cockpit organization; and should have all conceivably necessary approach plates in arms reach in case I need to divert. While I had read a lot about icing and its effects; I did not anticipate how quickly performance would degrade from such a brief encounter; particularly regarding the tail. There was never more than perhaps 1/4 inch on the wing; but likely more on the tail and that was enough for it to lose some of its effectiveness. I was glad that I diverted immediately and made a relatively uneventful landing; but I will be extra vigilant next time icing is forecast.

Data retrieved from NASA's ASRS site as of April 2012 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.