#159, without details of performance ‘tools’:- what is the basis of calculation, origin, who published them and the guidance for use, suggests weak knowledge ‘in the workshop’.
Blunt or rusty ‘tools’ are of little value; a key point about landing distances is that they are approximate (never really sharp), and that accuracy decreases with increasing ‘wetness’ and contamination.
Technical variation can be estimated, but the human contribution less so, especially in new or novel conditions. The conditions in each landing differ, we never experience the same landing twice; past comparison is of lesser value, but the lessons learnt should be, providing they are applied to the next landing.
Tools are best used by skilled craftsmen, according to circumstance, judgement - ‘the right way to cut the grain’.
BA ‘good’, is good relative to a wet runway. Wet performance is a projection, an estimate based on dry runways, which have a different version of ‘good’.
Consider how performance tables might accommodate the range of water depths up to 2.99 mm, but differ where 3 mm is defined as flooded (% of runway covered). The tables do not cover every combination, particularly when we consider runway surface texture, tyre wear; that’s why we have regulatory advice and the need for professional knowledge, and above all else the ability to apply professional judgement.
CT, I support your underlying view, but please there is no ‘legal’ value in performance, nor perhaps in anything we do in aviation.
There are required or recommended values, and most important, justifiable choices of action - these are the basis of your defence.
There is nothing legal about sitting in EMAS quoting book figures when the lawyers are speeding down the runway behind you, measuring the actual landing conditions (‘legal’ hindsight), and forming their judgement on how you handled the situation and aircraft.