I accept the need to present a professional image to both customers and visiting regulators, but I would offer this in an effort to mainatin some balance.
At a recent course that I attended at the head office of a certain aircraft manufacturer based in Seattle, ALL of the instructors wore smart, pressed, Chino style trousers, and good quality polo shirts bearing the corporate logo. This presented a professional and unified appearance of staff, and enabled them to instruct in a relaxed, (perhaps informal atmosphere) - which their own feedback had shown was what the Students preferred.
The tie, as far as I am concerned is no more than a strip of coloured cloth designed to hide my shirt buttons, and I would scrap it tomorrow if I could. However, I have flown with instructors who wear them with no problem. If my employer required that I wear one as part of a corporate image, then I would, reluctantly do so. I take the point about hot days too.
From a Health and safety perspective, perhaps we should consider wearing clip on ties, bearing in mind that there are many parts of an aeroplane that can trap a flapping tie?
Blue skies