Capn, #26 Thanks.
The QRH is of greater interest. Presumably the table ‘ref distance’ is used once all of the relevant corrections have been applied; then calculating and adding the safety margin >15% to give the expected landing distance.
The chart illustrated on page 25 looks like the basic Boeing format for ‘actual’ distances, which is open to debate whether this is realistically achievable, even before considering misjudged runway braking conditions. As I recall this was part of the background to the FAA’s recommendation for >15% additive (SAFO) because the assumptions in calculating the baseline distance were ‘best piloting performance’ in every circumstance.
The remaining question is what was the basis of the QRH distance used in the accident; has it changed (to OLD), and if so what additional distance is given by the assumptions in the OLD calculation; and are crews aware of any change?