Narrative:

Approaching airport ZZZ at 10;000 feet; found temperature lowering to 0 C. Requested lower and assigned 9;600. Temperature was between +1 C and 0 C. Radio reception with center was poor. Eventually called for center on 121.5. Approach replied with new center frequency. Called center and reestablished contact and got lower to 8;600. All of this occurred in IMC. As I reached 8;600 feet airspeed started to drop and then went to zero. I started to descend below 8;600 feet. Called center and asked for vectors back to ZZZ. I did not [request] emergency [handling]; but looking back center clearly treated me as an emergency. Center gave me vectors back to ZZZ. I found my pitot heat off. I turned it on immediately. Turned on the tks to max. I did not see any ice on the wings. Soon my airspeed for the pfd and the back-up airspeed appeared to be working again. Center gave me vectors for the ZZZ RNAV [approach]. Flew the vectors; got established on the RNAV and landed without incident. After I landed I looked at the airplane carefully and found no evidence of ice.chain of events.loss of radio - although I did not see ice; there must have been some. As I approached ZZZ and lost contact with center I should have requested an approach into ZZZ.pitot heat off - I still do not know how the heat got turned off. My only speculation is I was cycling the tks on and off to mitigate icing. I must have turned off the pitot heat instead of the tks during one of these cycling events. I; as a primary rule always have pitot heat on when in a cloud no matter how warm it is in the cloud.loss of airspeed indicator - when the airspeed indicator fell to zero; the autopilot begins to descend to avoid a stall. Audio alerts told me this. It took me a long time to recognize the pitot heat was off. But once the pitot heat was turned on the airspeed came on-line fast.not ready to make an approach - as I approached 8;600 feet; I was strongly considering landing in ZZZ. However; I had not started planning for this. Therefore I did not have the plates up nor have the procedure loaded.human performance1) did not recognize radio interference as a sign of other problems.2) did not react and plan quickly enough to plan for a way out before there was a problem; e.g. What to do if airspeed goes off-line.3) did keep caps (parachute) as an option and would have deployed if I came within 1;000 feet AGL; I believe the lowest I went was 7;900 feet or about 1;500+ AGL.lessons learned*very happy that I had done a dozen instrument approaches in the last 90 days. Being familiar with the airplane systems allowed me to program the approach rapidly while trying to understand why the airspeed went off-line. This was a high workload approach. Flying an approach into an unfamiliar airport even when it is routine is hard enough. But again know how to get the approach up on the display to review and programmed quickly and accurately helped a lot.*I should have asked for higher. I was fixated on staying below the freezing level. I should have asked where the tops were from a departing twin that I know went much higher.*weather forecast indicated to me that it should be possible to stay under the icing level for this mission. But when forecasts do not match flying conditions; need to make a change.*I am very happy I asked for center's help when I needed it. I told him what I needed and he helped. I wish I could thank that controller.landing turned out to be a non-event. Main problem was not having the pitot heat on while in the clouds which led to the air speed indicator going off line which led to the altitude deviation. I will now be even more careful to recheck the pitot heat is on while in the clouds.

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Original NASA ASRS Text

Title: SR22 pilot reported losing all airspeed indication in icing conditions and electing to divert to a suitable airport. During vectors to the airport it is discovered that the pitot heat is turned off. Turning it on quickly restored airspeed indication.

Narrative: Approaching airport ZZZ at 10;000 feet; found temperature lowering to 0 C. Requested lower and assigned 9;600. Temperature was between +1 C and 0 C. Radio reception with Center was poor. Eventually called for Center on 121.5. Approach replied with new Center frequency. Called Center and reestablished contact and got lower to 8;600. All of this occurred in IMC. As I reached 8;600 feet airspeed started to drop and then went to zero. I started to descend below 8;600 feet. Called Center and asked for vectors back to ZZZ. I did not [request] emergency [handling]; but looking back Center clearly treated me as an emergency. Center gave me vectors back to ZZZ. I found my pitot heat off. I turned it on immediately. Turned on the TKS to max. I did not see any ice on the wings. Soon my airspeed for the PFD and the back-up airspeed appeared to be working again. Center gave me vectors for the ZZZ RNAV [approach]. Flew the vectors; got established on the RNAV and landed without incident. After I landed I looked at the airplane carefully and found no evidence of ice.Chain of events.Loss of radio - Although I did not see ice; there must have been some. As I approached ZZZ and lost contact with Center I should have requested an approach into ZZZ.Pitot Heat off - I still do not know how the heat got turned off. My only speculation is I was cycling the TKS on and off to mitigate icing. I must have turned off the pitot heat instead of the TKS during one of these cycling events. I; as a primary rule always have pitot heat on when in a cloud no matter how warm it is in the cloud.Loss of airspeed indicator - when the airspeed indicator fell to zero; the autopilot begins to descend to avoid a stall. Audio alerts told me this. It took me a long time to recognize the pitot heat was off. But once the pitot heat was turned on the airspeed came on-line fast.Not ready to make an approach - As I approached 8;600 feet; I was strongly considering landing in ZZZ. However; I had not started planning for this. Therefore I did not have the plates up nor have the procedure loaded.Human performance1) Did not recognize radio interference as a sign of other problems.2) Did not react and plan quickly enough to plan for a way out before there was a problem; e.g. what to do if airspeed goes off-line.3) Did keep CAPS (parachute) as an option and would have deployed if I came within 1;000 feet AGL; I believe the lowest I went was 7;900 feet or about 1;500+ AGL.Lessons learned*Very happy that I had done a dozen instrument approaches in the last 90 days. Being familiar with the airplane systems allowed me to program the approach rapidly while trying to understand why the airspeed went off-line. This was a high workload approach. Flying an approach into an unfamiliar airport even when it is routine is hard enough. But again know how to get the approach up on the display to review and programmed quickly and accurately helped a lot.*I should have asked for higher. I was fixated on staying below the freezing level. I should have asked where the tops were from a departing twin that I know went much higher.*Weather forecast indicated to me that it should be possible to stay under the icing level for this mission. But when forecasts do not match flying conditions; need to make a change.*I am very happy I asked for Center's help when I needed it. I told him what I needed and he helped. I wish I could thank that controller.Landing turned out to be a non-event. Main problem was not having the pitot heat on while in the clouds which led to the air speed indicator going off line which led to the altitude deviation. I will now be even more careful to recheck the pitot heat is on while in the clouds.

Data retrieved from NASA's ASRS site 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.