CJ: Thank you for the clarification. I was almost certain that Chalky had been seconded to Boscombe Down (where my godfather also flew as a test pilot) but had not recalled that these 'trials' had occurred in Canada.
If I remember rightly he mentioned that these events took place at around 10,000ft and that more than once the Nr droop was so severe that they had to effect autorotation during which process, descending into slightly warmer air, they were able to regain sufficient effectiveness on the blade airfoils so as to sustain the auto and ultimately cushion the landing!
As my godfather used to tell me .. he and his kind had to venture beyond the aircraft's boundaries in order to ascertain exactly where they were. No computer modeling in those days!