It is against FOP. The key to that is there has to be a safety reason to do so. Taxing with them up and more specifically "turning" because that really is the key issue here, can cause misalignment of the canopy and stress parts.
Most of the time, it is understood if it is blazing hot, they will be up as even with cockpit air on high it's blowing desert hot air as cool as it can..
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