Sherm, I would not say the uses are distinct and understood as such by most speakers in the UK. Historic is much more commonly used to describe anything that is historically significant, or is attached to notable historic events. Historical is more likely to be used to refer to something that was relevant or true in the past, or a situation that no longer is the case. That in itself would be rare. The adverb is more likely to be used: e.g. "Historically, we used to serve both Heathrow and Gatwick Airports, but we only fly to Heathrow currently.