Re BPF 'This switching off of Carb heat on short final seems to be a unique to British flight training practice that seems to have been mindlessly passed down through the generations.
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I got my licence on the Australian syllabus and was taught to keep carb heat on until on the ground. When I converted my licence to a UK one, I was told to switch carb hear off at 200'. I've since seen this requirement documented in the order book of a flying club.
Interesting. I was taught to fly in UK and it was always carb heat on at pre landing checks until touchdown. Can't see for the life of me why you would be wanting to fiddle with something on short finals, or wonder whether you have or have not selected/deselected it. I've discussed this with friends who were taught to fly at various ATO's and they were all taught carb heat until touchdown.