Stuck_in_an_ATR :
Still, the basic requirement for commencing a visual app is to be able to see the runway throughout the maneouvre.
Are you 100% sure about this? I have never been able to find the runway requirement anywhere, and EU-OPS defines a visual approach as :
Visual approach. An approach when either part or all of an instrument approach procedure is not completed and the
approach is executed with visual reference to the terrain.
So in
theory I would think you could do a visual approach in 800m, if you are very, very familiar with the terrain around the airport (Not something I would ever do though
)