Flight Operations - COPA Corner - It's Still Here!

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by Adam Hunt, Canadian Owners and Pilots Association (COPA)

It has been years since I have seen this old hazard in aviation - I was beginning to think that it had disappeared, but, surprise, it is back when you least expect it! January16, 2005, started as a sunny Sunday morning in the Ottawa area. The temperatures were forecast to reach -8°C, so many pilots decided to take advantage of the slightly warmer weather and go flying. By early afternoon, the engine on our AA-1 Yankee had been nicely preheated and we were ready to start. By that time, the high clouds from an incoming system were turning the day duller in colour. A trace of stratus fractus was hanging around at 3500ft. The winds were almost calm; surface temperature was -10°C with a dewpoint of -17°C.

We took off and climbed up to 3000ft on our local flight, calling terminal in the climb. Levelling off, I set cruise power at 75%, but, within a few minutes, the RPM was bleeding off. I pulled on the carb heat and the RPM bled off even more - “splutter, splutter,” and then the power came back quickly. Carb ice, on a day like this? Odd. A few minutes later, it was back so we decided to leave the heat on “hot,” as this wasn’t clearing up.

The rest of the trip was uneventful, except for the higher fuel burn due to the almost continuous use of carb heat to keep the ice at bay. Returning to home base, we were informed that a student pilot flying a Cessna150 was stuck on the runway. The 150 wouldn’t start after having “flamed out” on the ground during a touch-and-go. A stream of aircraft coming home decided to hold in the local practice area while the Cessna was pulled off the runway.

The culprit? Carb ice again - a long final approach at reduced power with the carb heat off, and the engine stopped on the runway. After the plane was cleared, the rest of us returned without incident for landing. While paying for fuel at the flying school, I talked to an instructor there. She had been up flying for much of the day in the school’s 150s, and had also seen lots of carb ice - more than in a very long time. Other pilots reported carb ice too. Even some pilots flying ultralights with two-stroke engines that are normally pretty “carb-ice-resistant” (and are not carb-heat equipped) returned home with rising exhaust gas temperatures (EGT).

The carb ice didn’t give up easily. After refuelling at the pumps, we started up to taxi back to the hangar line. The engine started fine, but balked on throttle increase. Some more carb heat cleared that up quickly and we got the Yankee back to the hangar without any further icing incidents.

What a strange day - carb icing was not suspected, based on the surface temperature and dewpoint, nor after consulting the carb ice chart found in section AIR2.3 of the Transport Canada Aeronautical Information Manual (TC AIM), but it was found everywhere by almost everyone flying piston engines that day. Many of us haven’t seen carb ice in decades - we were beginning to not believe in it anymore!

The lesson is clear - check for carb ice regularly, even when you don’t expect it, and watch your RPM carefully (or manifold pressure in constant speed prop-equipped aircraft) for the telltale signs of power loss. Get the carb heat on first when you do! More information about COPA can be found at http://www.copanational.org/.

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