– Wing tip rotors move outwards at about 5kt.
– Turbulence behind aircraft is dangerous in light crosswinds, i.e. crosswind pulling one rotor onto the centreline.
– Current ICAO regulations require 2 minutes or 4nm clearance for a heavy aircraft behind a heavy aircraft on approach or departure.
Windshear at Inversions
Inversion produces a very sharp boundary between the airflow above and below it.
– A free-stream wind of over 40 knots means turbulence in the boundary layer and over land. There will be at least a 20kt speed and 40 deg heading difference between the surface wind and the free-stream wind.
– A temperature inversion of 10 deg C or more in the first 1000 ft agl will completely isolate the slow surface wind from the fast free-stream wind above the inversion giving marked windshear in the climb or descent and clear air turbulence near the top of the inversion.
– Turbulence inversion will also produce a sharp windshear. Turbulence cloud below the inversion if present is probably SC with moderate to severe turbulence.