This is very sad. A couple of guys out with their mates in other microlights for a fly-out on what seems a lovely day and it ends in such tragedy.
A few years ago we were flying to Caernarfon in a Chipmunk. Surface wind at Caernarfon was less than 5 kts, so I was taken by surprise when downwind of Snowdon, north of the field following the Menai Straight, we entered the most severe turbulence I have ever experienced. The aeroplane was thrown about in all axis as well as vertically up and down. The stick and rudder seemed almost ineffective and wisps of rotor cloud formed and dissolved around us in the otherwise clear but tortured air.
I hardly had control of the aeroplane, but managed to turn away from the hills and descend, until thankfully we entered calmer air. Whatever the wind speed over the Snowdon range it was a heck of a lot more than 5kts! 40 or 50 would be nearer the mark! The venturi effect must have been boosted not only by the terrain but by the air mass above the mountains.
A similar but much smoother venturi effect caught a friend of mine instructing in a C150 at night in the Peak District. Surface wind at Manchester (who were vectoring them) was calm, yet they were forced down, despite selecting climb power and flap, in very strong mountain wave into the lee side of Kinder Scout, escaping with moderate injuries (the aeroplane was wrecked).
You don't have to fly within a few hundered feet downwind of a big mountain to get into trouble if there's a locally very strong venturi-induced wind.
Last edited by Shaggy Sheep Driver; 10th Jan 2013 at 20:38.