Be aware of the tendency to descend when turning towards a valley, and to climb when turning towards a hill. The latter can kill you easily.
Visual illusions! Certainly when HM the Queen paid for my helicopter training, mountian flying was a mix of visual and instrument flying...there are any number of false horizons out there in the hills to get your brain all confused. Sloping strata in the rock, sloping ridgelines even sloping cloudbases can give you a false horizon so crosschecking the artificial horizon every couple of seconds was a must, as was ensuring the VSI was on zero if you wanted to fly level (as in a circuit to a landing point). I remember having an inadvertant 500fpm climb downwind just because I was next to a sloping stratum.
There's a lake in Snowdonia somewhere that looks like it has a sloping surface because of the visual illusions (great for water skiing though - who needs a boat!)
And one of my training mistakes... with a (simulated) engine failure turn downslope, it gives you so much more time than turning towards rising ground!
And respect the wind and fly on the updrafting side of the valley...we sat in a Wessex in updrafting air with the tailwheel on a rock and the collective lever almost on the floor, using less torque to hover in the updrafts than it took to turn the rotors while stationary on the ground.
Remember wind doesn't go underground (unless Arthur Scargill has been on the baked beans) so if caught in a downdraft it will eventually stop - see pass crossing story above - you just may be quite close to the surface by then.
Cross at 45 degress also applies to big power lines if you happen to be stooging around at 200ft (looking for somewhere to do a precautionary forced landing...of course)
There's lots more, get a good instructor, PFA Coach Charlie Huke would be a good place to start, he used to teach mountain flying at the SAR Training Unit.
Cheers
Russell
