Mike
If you take a mass of water like the thames surround that with frozen buildings and nil wind that is condusive to sporadic fog and low mist conditions.
The aviation expert quoted freezing fog and icing effecting helicopters yes if the aircraft is flying in that fog ie IFR and in IMC but I presume that very low level the pilot will be staying visual albeit at times with minimal visual reference and maybe pushed down in trying to maintain visual reference.
Very easy to miss an unlighted crane or one concealed in mist and low cloud.
Last edited by Pace; 16th Jan 2013 at 09:36.