An Interesting topic and a tale from Vietnam as told to me by the Pilot who flew it. Mike Gralian (Sacramento California) was a Maintenance Officer with I believe the 1st Cav. He took minimal crew on board for a topping check in a UH-1. Basically a handful of collective and off We go to get some reading on the guages.. Problem turned out to be the aircraft had just come out of extensive maintenance and someone ( Murphy) had installed a bolt in backwards allowing the long end of the bolt to get in the way of the collective. When they were at a point ready to descend, collective would not go down. According to Mike it was panic city for many minutes. Aircraft continued to climb. He stated it was somewhere near 18000 feet that in desperation the crewchief actually stood on the collective. (You can move around in the Huey). That extreme move was enough to free the thing without losing the rotor head from sudden down collective.
Anyway they all survived and headed for the club on landing.
Things like this do happen.