While most light-airplane icing encounters are safely and successfully resolved, theres no such thing as a little ice on them. After years of thinking a trace here or there-or even a quarter-inch or so-was no big deal, I recently discovered one reason for known-icing approvals.
It was a crisp, brisk fall day over Arizona; I was flying my Bonanza east from California and planned to stop in Winslow, Ariz., for fuel, a snack and to stretch my legs. Somewhere between Prescott and Winslow, on an IFR flight plan, I encountered some benign-looking clouds at my altitude. Although the outside air temperature was below freezing, I thought nothing of punching into these white, puffy clouds. I had plenty of altitude, there was much warmer air below me and I thought it would be interesting to see what, if any, ice they could generate. I also wanted to refresh my memory on how the airplane handled a little bit of ice.
Sure enough, the two clouds I flew through deposited some clear ice on the windshield and the wings. Presumably, other parts of the Bonanza had some ice on them, also. Although I was in the clouds for just a few moments each, they left their mark and-even though it still only qualified as a trace-I was a bit surprised at how much ice the airplane had picked up.
Since I was close to Winslow, I asked for and began a slow descent. My approach and landing were unremarkable and I taxied to the self-serve pumps. Although most of the ice had melted, some still adhered to the airplane, affording me a small badge of honor.
As I climbed out, I heard a hissing sound. Thinking it was coming from the self-serve fuel pumps, I tried to identify the source but realized the sound was coming from the airplane. Indeed, fuel was venting overboard. Thats odd, I thought, and opened the main fuel tank. I was greeted with a whoosh as air pressure in the tank equalized; the hissing and venting stopped.
That little bit of ice I encountered had plugged the fuel vent on the tank feeding the engine. To equalize pressure, the system eventually started venting fuel overboard. If I had been flying a max-range trip, I would not have had the planned fuel aboard.
While many light airplanes may carry small amounts of ice quite nicely, theres no way to know if some system or another is being affected by the accumulation. In this case, the lack of a heated fuel vent-which can be required on aircraft approved for flight in known icing conditions-is one of the differences between an airplane approved for those conditions and one merely sporting a warm pitot tube.
