During my 35-year flying career, I have experienced my share of carburetor icing, but nothing remotely like what occurred on both legs of a cross-country between Penn Yan, New York, and Lebanon, New Hampshire, in April/May 2014. When I encountered carburetor icing previously, it presented as the classic slow degradation of performance scenario. Application of carb heat made the engine run rough for a few seconds before clearing, at which point I could resume normal operations or, in some cases, leave carb heat on if the problem was persistent. As additional context, most of my serious cross-country time has been in fuel-injected airplanes, in either a Piper Arrow or, more recently, a Cirrus SR20.
This trip was in our flying club’s Piper Cherokee (PA-28)—my first trip in a carburetor-equipped airplane since 2010. The outbound leg featured dismal weather at departure with clearing toward New Hampshire, and after being in and out of clouds and light rain at 9,000, I was enjoying visual conditions. Thanks to a warm front, the temperature at 9,000 was 5 degrees C. As my destination drew near, Boston Center cleared me from 9,000 to 7,000 feet, and I reduced power from about 65 percent to 45 to 50 percent for a gradual descent. I did not apply carb heat, possibly because I never understood how important this was in the letdown phase, or possibly because I did once understand but was rusty. In either case, the lesson was immediately learned, since as soon as I moved the throttle there was a loud pop and sudden decrease of power. I immediately applied carb heat, adjusted power and mixture, and the engine came back to life. The remainder of the flight was uneventful, but I was careful to apply carb heat prior to further power reductions.
Ice was on my mind for the return flight, but this time it was airframe icing. Having filed the return leg for a late-afternoon departure at 8,000 feet, I learned from my preflight briefing that there was an Airmet Zulu for the entire leg with multiple cloud layers through 13,000. No pilot reports were available. The forecast temperatures aloft were minus 4 degrees C at 8,000 and minus 1 degree at 6,000, with ceilings on the surface reasonably high. My primary plan was to try 8,000 first, use 6,000 as a Plan B, and be ready to execute the nearest instrument approach to VFR if that didn’t work out. I figured I could complete the return leg VFR or, if not, spend the night on the ground making new friends.
The departure from Lebanon was VFR, and climbing through 6,000 I started to go into clouds. Continuing the climb to 8,000, I got a first quick burst of light rime that put me into the I-am-paying-attention state, and then I picked up a second short but more intense burst. I had had enough fun. While still at cruise power as I was about to ask Boston Center for 6,000, the engine suddenly unwound. Unlike the previous pop and loss of power incident, this felt as if I was smoothly but quickly reducing power to almost idle. My sense was that as serious as the first encounter was, this was worse, and my eyes started focusing on terrain below the broken layer. Fortunately, carb heat once again saved my bacon, and I was able to continue the flight at 6,000 with no further airframe icing (temperature was hovering around zero). I flew the remaining two hours with carb heat on and was happy to accept the performance and fuel- burn penalty.
As soon as I was able after returning, I reported the incident to our flight safety board and also corresponded with Gene Benson, whose wisdom I have gratefully received in various AOPA-sponsored webinars. I learned that I was in a much more hazardous carb ice regime than I understood and the PA-28 can be particularly problematic. I also reviewed FAA literature and accident reports. The positive here was that my instincts were good and I did not fall prey to the all-too-common trap of applying carb heat and then backing it off too soon. The bad news is that had I been more attuned to recent knowledge, I would have been better aware of the risks during my flight.
