re TAC57, my not-long-after-the-spot account reads:

16 June 1989 Ben Aden east ridge about 1730 "gained a rocky platform and as we paused we heard the sharp sound of blowing plastic sheeting (or a flapping tent!) from just above. "it" came over the lip, marked its slow passage with a flattening of the grass a couple of yards from us, went down the inside of the shelf, and hit a low parapet at the end with a loud crack. a wholly novel experience, aptly described by Richard as a 'windflap'; wondered what sticking an arm in its path would have felt like. R encountered one two days later which sent a butterfly spiralling aloft. odd in fairly light general winds - must be the terrain. climbed to another larger platform just below the great prow which had us both reaching for Lost World and Roraima epithets..... thence in thick cloud along the spine...the dry mist parted once..." it was quite warm I recall, as my taste in T-shirts came under criticism.
a newspaper Weatherfile piece soon after described this as a 'calm-weather whirlwind typical of hilly country' in discussing crop circles (oh no!).
since then I have met several lesser versions, and am pretty sure the Kintail missile can be interpreted as a multi-sensory illusion. although the vortex travels quite slowly, the apparent speed is very high (given reaction time to the unexpected, and post-rationalisation time) - as with any sound source going 180 degrees past you very close by in a second or so.
I remain curious as to why an upward moving heat column (butterfly) appears to flatten the grass. presumably this is due to air being sucked in at ground level, so the grass is being laid flat from all sides in a spiral sequence, not squashed from above.
it is notable that all your reports and my case are in the heart of the Western Highlands where the terrain is most extreme, and meteorological gradients are also steepest (mountains closest to sea and to high inland terrain). it is no coincidence that this is the area where I have observed almost all evidence of lightning strikes - hence the OS abandonment of the Sgurr na Ciche trig point, this TAC. (have you covered that subject before?). and Kintail is the seismic hotspot of Britain currently.

David Jarman
Mountain Landform Research