Fascinating calculations,
OpenCirrus619, and, to my mathematically unpracticed eyes, they seem good as far as they go; however, they address only part of the question.
The crucial aspect is at what percentage of the TORA should you make your decision (based on your second graph), so that you can stop within the remaining distance? Also, does that point not vary with the power/weight ratio of the particular aircraft? Surely, any calculation must also depend on braking effect and take into account the type of surface and conditions?
With so many variables, I wonder whether you really can arrive at a rule-of-thumb answer that is safe to use across the board?
JD
