The principles for determining landing distance (UKCAA perspective) are in
AIC 14/2006.
Although most modern aircraft are certificated with the ‘arbitrary’ method, see CS25/FAR25, the original 737 might have been certificated with the ‘reference’ method and grandfather rights claimed for all variants thereafter.
The current European requirements are in
CS 25.125 (~page 25). FAR 25.125 is similar, if not identical.
Change in thrust and other information is in AMC 25.125 (~page 267):-
“No changes in configuration, addition of thrust, or nose depression should be made after reaching 15m (50 ft) height.” For most aircraft this probably means idle thrust from 50ft.
Operational requirements EU (IR)-OPS / FAR 121, require the certificated distances (AFM) to be factored for dispatch according to runway/weather conditions.
IR-OPS – check this ref.
Operational requirements for in-flight pre-landing assessment of the ‘required’ landing distance are open to various interpretations and any factoring is usually based on un-factored manufactures data (QRH) which may differ from the certificated distances (read the QRH small print). There there are differences in the requirements for assessment and factoring between EU and FAR.
Furthermore, most manufacturers are now implementing ‘new style’ Operational Landing Distances (OLD) which provide more realistic data for a range of conditions; this may be published (QRH) with factors as 'FOLD'.
http://sapilot.com/a320/otherfile/In...erformance.pdf