Narrative:

We started back to our home airport; but decided to stay at an airport enroute due to weather; namely wind and icing possibilities. We departed the next morning. I had looked at my pireps and I saw two pireps; one area that showed negative or trace ice. I don't remember exactly if it was one or the other. We descended from 7000 ft. Which was clear to 4000 ft. And started picking up ice. I received a call at from approach which said an MD80 was picking up light rime at 3000 and the temperature was -3C. I acknowledged and said I was picking up ice at 4000 ft.; the ice was not light; it was moderate. When the accumulations were about 3/4 inch; I activated the boots. I looked out my left side and saw that the ice had come off and continued on with my duties. A little while later; my wife; who is a pilot asked if I was going to blow the boots as I said. I said I did already and she said no ice came off my wing. I looked over to see now a much bigger build-up of ice on the wing. My first thought was that we had lost a vacuum pump as I had double vacuum pump failure once before 17 years ago activating the boots. I immediately took the plane off auto pilot because of the potential of vacuum failure. There was no indication of vacuum failure on the vacuum gauge so I went back to thinking it might be a short in the boot switch.while I was hand flying the plane; I am moving the boots switch back and forth to see if I can get some movement or some clue on the right boot. I then started to wonder about the tail but then decided that was minor compared to asymmetrical ice weight and aerodynamics. The more I played with the switch; the worse the differential got as the left wing kept clearing the ice. I am guessing that at this time there was probably an inch plus of ice on left wing. The ice seemed to be coming at a faster rate as we progressed on the approach. I noticed my airspeed was lower than what it should have been given my power settings. I looked out and saw ice partially covering my pitot tube. I looked down at the pitot heat switch and noticed it was turned off. I must have bumped it off playing with the boot switch next to it. I told my wife that we were going to fly off of GPS and subtract 10 knots for the wind which was reported at 340 at 8. I told her I just wanted to keep the speed at about 130 which is much faster than I normally fly the approach; but I knew if there was a problem it would come at a slower speed. I had flown that approach hundreds of times and it is over an area that I grew up in so I knew there was no towers or obstacles that were higher than the 700-1000 ft variable ceiling that ATIS broadcast. My focus then was just to get out of the ice as quickly as possible. We got lucky at about 2000 feet when we broke out of the clouds into a long; almost like a tunnel of clear air. I had decided to stay in the tunnel as long as possible while approaching the airport. We were drifting left of course but I was clear of clouds and I stayed in that attitude until I looked over until I could clearly see the airport. The tower asked me if I was ok as I was left of course. I gave them a one word response of 'correcting' as my issues were not getting to the airport but what I would do once I got to the airport. I had decided to do the approach to landing at 120 knots or so with no flaps until I got down to ground effect; kill the power and hope for the best. The heavy wing was upwind of the crosswind so I thought that would be a plus. What surprised me; is after all the analysis that I did for the last four minutes or so went out the window when I made a snap decision to add 10 degrees of flaps at 1/2 mile out. At this time; I still don't know if that was a plus; a minus; or irrelevant. I do know that I routinely practice crosswinds with 10 degrees of flaps but never with zero degrees so I think I just naturally gravitated to my comfort zone. Within an hour of landing; I called my mechanic; described the situationand asked him to look at the airplane and when he tears it apart that I would like to be there so I could physically see the systems and air routing in case this happens again. I've had to use the boots only three times in 20 years of ownership of that plane and twice I went backwards in safety.

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Original NASA ASRS Text

Title: While flying in a Cessna Skymaster T337 in icing conditions the right wing de-icing boot failed to de-ice the wing.

Narrative: We started back to our home airport; but decided to stay at an airport enroute due to weather; namely wind and icing possibilities. We departed the next morning. I had looked at my Pireps and I saw two Pireps; one area that showed negative or trace ice. I don't remember exactly if it was one or the other. We descended from 7000 ft. which was clear to 4000 ft. and started picking up ice. I received a call at from approach which said an MD80 was picking up light rime at 3000 and the temperature was -3C. I acknowledged and said I was picking up ice at 4000 ft.; the ice was not light; it was moderate. When the accumulations were about 3/4 inch; I activated the boots. I looked out my left side and saw that the ice had come off and continued on with my duties. A little while later; my wife; who is a pilot asked if I was going to blow the boots as I said. I said I did already and she said no ice came off my wing. I looked over to see now a much bigger build-up of ice on the wing. My first thought was that we had lost a vacuum pump as I had double vacuum pump failure once before 17 years ago activating the boots. I immediately took the plane off auto pilot because of the potential of vacuum failure. There was no indication of vacuum failure on the vacuum gauge so I went back to thinking it might be a short in the boot switch.While I was hand flying the plane; I am moving the boots switch back and forth to see if I can get some movement or some clue on the right boot. I then started to wonder about the tail but then decided that was minor compared to asymmetrical ice weight and aerodynamics. The more I played with the switch; the worse the differential got as the left wing kept clearing the ice. I am guessing that at this time there was probably an inch plus of ice on left wing. The ice seemed to be coming at a faster rate as we progressed on the approach. I noticed my airspeed was lower than what it should have been given my power settings. I looked out and saw ice partially covering my Pitot tube. I looked down at the Pitot heat switch and noticed it was turned off. I must have bumped it off playing with the boot switch next to it. I told my wife that we were going to fly off of GPS and subtract 10 knots for the wind which was reported at 340 at 8. I told her I just wanted to keep the speed at about 130 which is much faster than I normally fly the approach; but I knew if there was a problem it would come at a slower speed. I had flown that approach hundreds of times and it is over an area that I grew up in so I knew there was no towers or obstacles that were higher than the 700-1000 ft variable ceiling that ATIS broadcast. My focus then was just to get out of the ice as quickly as possible. We got lucky at about 2000 feet when we broke out of the clouds into a long; almost like a tunnel of clear air. I had decided to stay in the tunnel as long as possible while approaching the airport. We were drifting left of course but I was clear of clouds and I stayed in that attitude until I looked over until I could clearly see the airport. The tower asked me if I was ok as I was left of course. I gave them a one word response of 'correcting' as my issues were not getting to the airport but what I would do once I got to the airport. I had decided to do the approach to landing at 120 knots or so with no flaps until I got down to ground effect; kill the power and hope for the best. The heavy wing was upwind of the crosswind so I thought that would be a plus. What surprised me; is after all the analysis that I did for the last four minutes or so went out the window when I made a snap decision to add 10 degrees of flaps at 1/2 mile out. At this time; I still don't know if that was a plus; a minus; or irrelevant. I do know that I routinely practice crosswinds with 10 degrees of flaps but never with zero degrees so I think I just naturally gravitated to my comfort zone. Within an hour of landing; I called my mechanic; described the situationand asked him to look at the airplane and when he tears it apart that I would like to be there so I could physically see the systems and air routing in case this happens again. I've had to use the boots only three times in 20 years of ownership of that plane and twice I went backwards in safety.

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.