English: Contrails over London, looking West from Clapham (in the general direction of Heathrow Airport). The sheer number of trails give a sense of the enormous volume of traffic through the airspace. In general if you can see a trail the flight is at high level and almost certainly not landing at the local airport. The trails going right to left in the picture are from Manchester or north thereof with destinations in France or beyond. Bends in the trails show changes in course taken by the aircraft avoiding traffic on instructions from controllers or just following approved routes.