Really helpful links to these valuable presos and papers alf5071h, thank you. I'm datamining right now and being a one-man band need all the help I can get in assessing and presentation of overrun risk. I've seen Pere Fabregas' (of Vueling), presentations in other links and consider them of great interest as they are the first attempt I've seen to turn actual landing distances into expressions of threat, (of runway excursion) and subsequent risk assessment. The FAA/PARC paper is of exceptional interest.
Your caution regarding the quality of data is a good one, and I would include in this the innate inability to accurately determine the touchdown point on non-GPS-equipped aircraft.
With the exception of Vertical 'g', sample rates for parameters normally used to determine touchdown are not frequent enough to accurately determine the point of touchdown. At speeds of 160 to 200fps, the best accuracy one can expect is +/- 360 to +/- 400 ft, meaning the touchdown point indicated in the data can be between 700 and 800ft "in error".
This means that determining runway remaining will also be in error and I haven't seen a successful way of fine-tuning this fundamental issue. The old method of assuming that the airplane is "over the threshold at 50ft RA" isn't good enough.
The mathematics behind using the glideslope make the t/d point a bit more accurate as does the determination of where the glideslope antenna is located and how far the airplane travelled past it to touchdown but it is still not as accurate as desired.
If anyone has thoughts on this basic flight data issue I welcome them. In the meantime, both touchdown distances past the threshold, and runway-remaining distances and related event should, in my view, be viewed broadly rather than statements of high accuracy in non-GPS equipped aircraft.
I think that perhaps a more valuable number might be the flare times and distances, primarily because we know that when the thrust levers/throttles are closed, the airplane is definitely over the runway and a landing is intended. Measuring from say, 20ft flare height, to touchdown will tell us how much runway was used in the flare and as such may be more useful, although we still will not know where on the runway the airplane has touched down.