The crux of the discussion involves differing definitions, and how theory is related to practice.
There are many regulatory and other guidance documents requiring update after the TALPA changes (operational landing distances).
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The 'TDZ' (fixed distance runway markings) is not related to actual runway length, thus there is no relationship with the aircraft landing performance, …."
In this sense TDZ is defined as a marked distance along the runway which can be identified but not related directly to expected performance.
Alternatively, 'Touchdown Zone' as an idealistic area in which the pilot aims to touchdown; the position is only identified after a landing, where aircraft actually touchdown. It involves air distance - a variable, and other variations including piloting techniques. The touchdown position is important in landing performance, but never fully assured as a fixed point. cf aerial photos of dispersion of rubber markings.
Landing performance is assessed using reported conditions; many factors are variable, e.g. reported wind (+-2), vs actual headwind (+-?) n.b Funchal, may need more than the minimum 15% safety margin.
The derivation of landing performance is in AMC CS 25.1592.
Para 3.0 lists 'standard assumptions' which contribute to variability. Note paras 5.0 and 6.0 … [page 28 …]
" … assessing the landing performance at the time of arrival using procedures for operation in service. These procedures should: — be able to be consistently executed in service by flight crews of average skill; — include safe and reliable methods or devices; and — allow for any time delays that may reasonably be expected in service.
The air distance that is used for any landing at any runway is a function of the following variables: — runway approach guidance; — runway slope; — use of any aeroplane features or equipment (e.g. heads-up guidance, auto-flight systems, etc.); — pilot technique; and — the inherent flare characteristics of the aeroplane.
… analytically determine the air distance that is used for operational assessments of the landing performance as ‘the distance that is traversed over a period of 7 sec at a speed of 98 % of the recommended speed above the landing threshold’.
The recommended ‘speed above the landing threshold’ may also be referred to as the ‘final-approach speed (VAPP)’. The above air distance represents a flare time of 7 sec and a touchdown speed (VTD) of 96 % of the VAPP. The VAPP should be consistent with the procedures recommended including any speed additives, e.g. those that may be used due to winds or icing conditions.
… also provide the effects of higher speeds, to account for variations that occur in operations or are caused by the operating procedures of individual operators."
The realty of operations is indicated in an FAA study of landing performance; note the range of values, section 4.3 onwards [page 28 …].
The key influencing factors are also in FAA AC 91-79 Mitigating the Risks of a Runway Overrun Landings.
Aircraft landing distance is not related to TDZ; it could with calculation dependant on specific conditions, but never assured due to the situational variabilities and pilot performance.
Beware SOPs based on TDZ runway markings - exceptions for specific runways with special markings e.g Vagar EKVG 'Touchdown in the yellow box, LCY before the fixed line \ lights'.
AMC CS 25.1592, page 26 …
https://www.easa.europa.eu/en/downloads/134260/en
FAA A Study of Normal Operational Landing Performance on Subsonic, Civil, Narrow-Body Jet Aircraft; page 29 …
https://www.tc.faa.gov/its/worldpac/techrpt/ar077.pdf 5 M/s ≈ 10kts
AC 91-79 Mitigating the Risks of a Runway Overrun Upon Landing
https://skybrary.aero/sites/default/...shelf/3606.pdf
ICAO Doc 10064 - Aeroplane Performance Manual, page 12 … and particularly the Appendices
https://www.sapoe.org/wp-content/upl...Task-Force.pdf