My guess would be never? If you are on terrain that steep, you would likely accelerate out of control too fast. But perhaps if you landed on a more moderate section and slowed, you might be able to stop before the next steeper section or a cliff, assuming you weren't too injured? I haven't climbed Triple Couloirs and can't comment on that route specifically. My point was that it's easy to get complacent with certain skills and a fraction of a section of reaction time can be the difference between arresting and a fatal fall. Think about those who have died descending Aasgard Pass because their glissade got out of control. Again not saying this accident was caused by complacency etc. and I assume anyone who attempts to solo Triple Couloirs is up for the task. We have all "4th classed" terrain on approaches or descents when the rope has been put away and gotten away with it, and we have pulled certain moves unroped that, if blown, would have led to tragic outcomes. I respect the doctor for getting after it in his 60s. It could have been any of us.