JS, thanks for the info, I had overlooked AC 121.195. This is an extremely old AC, which IIRC was designed primarily for operators to obtain accurate wet (certificated) landing data. I am not aware of any manufacturer or operator using certificated data based on this standard.
As for Boeing or third party ‘actual’ data - published in the QRH (non-certificated), it is necessary to read the small print very carefully.
This data would not appear to meet the requirements of EU OPS-1 for pre-dispatch assessment. Furthermore if it were to be used in the EU OPS-1 pre landing check
“to ensure a safe approach and landing”, it might be difficult to define a suitable additional safety distance factor which would equate to a level of safety implied in the pre dispatch calculations. Hence my post #12.
In the event of an incident in normal operation, reliance on reverse as in the QRH data, could be difficult to justify given the lack of reverse credit in certificated data.
Obviously in non-normal / emergency conditions the QRH data is invaluable, but this still requires knowledge of what assumptions are in the performance calculations, e.g speed and threshold accuracy and assumed touchdown position (which may not be achievable).
Whilst the recommendation to add 15% to wet/slippery performance (ill-defined terms) will aid safety, this margin may only result in a realistic minimum achievable landing distance, thus an additional safety margin should always be considered. Many operators / pilots see this recommendation as a necessary and legally sufficient minimum, which unfortunately several overrun accidents have shown not to be the case.
There are many gaps in the regulations and guidance material on this subject. It is difficult to quantify a specific distance margin or factor for every situation, thus the reliance on human judgement of ‘safe’ in the conditions perceived. Unfortunately the human suffers weaknesses in perception and judgement, but is also subject to incomplete data about runway condition and the assumptions in advisory landing data.