We used carby heat on for all low power descents including landing approach, with thousands of approaches each year between a fleet of up to 10 warriors it never posed a problem. There was one instance of a throttle getting stuck so badly during a solo flight the student physically bent the lever trying to increase power, but happened early base so the quick thinking student turned to final early and made the field with no issues. Engineering inspection post flight found no mechanical defect leading us to think it was throttle ice had locked up the mechanism and the student said they had not used carby heat. Other causes of failures in this area I have heard of is students moving fuel selectors to off on downwind instead of changing tanks, also moving the mixture rearward instead of the throttle when turning base. I have had carby ice when flying just under cloud base on a few occasions in Warriors at cruise power, quick application of carby heat and power quickly returned. Older engines some pilots can easily miss identify oil/lead fouling of plugs after prolonged descents as carby ice. That shouldn't happen in the circuit unless somethings really wrong.
Have to also remember that the carby ice graph is not related to ground temperature but actual OAT at the altitude you are, and the closer you get to the cloud base the closer to 100% humidity you get. So while it might not be likely on the ground, it could become far more likely at altitude. And then after engine shut down heat soak and OAT will melt any evidence of it.
PS the operator I worked for had a long history with PA28s having imported several new in the 70s, and still operated some of those through to the 2000s. Never got to operate a Warrior 3, but apart from some small changes they seemed pretty much the same thing with no bench seat and the battery relocated to the engine bay, same engine and carby as far as I'm aware.
Last edited by 43Inches; 21st Nov 2022 at 23:26.