Thanks for those contributions, Nickkappos.
Devil, you make a valid point. In the smaller helis with hyd systems that can't cope with all flight envelopes it's accident potential that perhaps should not be tolerated in a/c design at all. This is refering Jackstall though. Any further comments on Hyd Lock appreciated. Perhaps someone knows the facts behind the scary clip from the beginning of the thread..which could easily have been an accident..
here Is this Jack Stall or a Hyd Lock...? Is it common?