My memories of auto-rotating a Whirlwind on the short pre-Harrier course at Shawbury have well faded, so could someone (patiently) explain the aerodynamics whereby it has been said that a stalled rotor disc could bring itself to a standstill? Surely even stalled there is still a rotational force on the blades which would keep the disc turning if air is passing through the disc (ie heli falling)? AAIB were, it seems, presumably deliberate in stating that neither main or tail rotors were rotating at impact, which is a concept I find hard to grasp.