Recently re-read a Canadian ATSB investigation about a year old, on a B206 Free Wheel fail, during a 180 auto, on opening throttle to full, the F/W did not engage, the RRPM decayed in the bottom flare despite full throttle. The F/W then did engage suddenly, but the slowed rotor caused the engagement with the full RPM engine, to be so violent it sheared off the rotor mast just below the main rotor hub, like a sort of torque overload induced mast bump...same effect, whole rotor blades and hub break away!
The crew were close to landing in the flare, so very fortunately walked away! Probably on pretty wobbly legs! I heard another one of these occurred recently? Finland? The F/W unit was found to be corroded internally by water contamination, exactly how, was not certain. But: To me, a significant factor was that a restrictor orifice in the MGB oil system blocked up with debris at some earlier stage, due the corrosion contamination apparently, preventing F/W lubrication. I feel this is arguably the straw which broke the camels back. The interesting thing is this. Bell Helicopters put out a NON MANDATORY modification, to replace the restrictor orifice with a small filter which would still catch any debris, but still allow oil through to lubricate the F/W. Seems to me, that's a pretty essential modification?? Now I need to try find out if the two B206 BIII's we use for our training still have the restrictor fitted, or the filter
....Autorotation's anyone? I have to fly some with students tomorrow! Comments?