H d. #9, the internet enables a range of opinions, but without justification they are of little value in a professional forum.
The certification requirements are in CS 25; guidance as to how these regulations can be met is given in advisory materials, e.g. AC 25-7B.
There are several acceptable methods for determining landing distance, which can consider the landing as separate segments. The air distance from 50 ft to touchdown, a transition distance, and the brakes on to stopping distance. These segments are 'stitched' together (as they are often tested in isolation) to form an acceptable model of the aircraft performance; this is the basis of the manufacturers' data (AFM).
An operational view of this is given in
AIC 14/2006 Landing performance of large transport aeroplanes –
‘This gross distance should be regarded as a theoretical minimum, consistent achievement of which requires a high level of pilot skill under favourable conditions, and concluding in a level of deceleration that would normally be considered excessive from the passenger comfort point of view’.
The AIC continues with practical advice for operators, noting that although it is still current it relates to JAR-OPS. One contentious issue is the allowable speed margin at the threshold, which may only apply if all other variables are at the datum value.
Note and heed the concluding remarks in the summary.
Guidance for the performance for light aircraft (perhaps more related to a private operation) is in
AIC 127/2006.
Paras 7 - 7.7 ‘
Safety Factors: it is recommended that the public transport factor should be applied for all flights. For landing, this factor is x 1.43’ (propeller aircraft factor?)
Also see ANNEX - landing and notes 1 - 3.
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