Current orations, post TALPA, using Operational Landing Distances (OLD), should not require use of factored landing distance as the primary data source.
Landing performance for pre landing assessment should be based on EU-OPS, CS 25.1592 or AC 25-32 (EASA operational requirement, FAA recommendation).
The recently amended AC 91-79B publishes factors to estimate landing distance if OLD are not available; the factors range 1.67 to 5.1 according to reported braking action and aircraft type ( lines … a matrix in the sand ). The basis of these is the ICAO Manual of Aircraft Performance, doc 10064.
Note the amended Chapt 3 (AC 91) re use of most adverse report of braking action or expected conditions, the 15% minimum factor applied to OLD may be inadequate in some conditions; plan for the worst case conditions i.e. RCR - 1
Also note tech assumptions about braking performance ("…
to create a reasonably conservative relationship between this engineering scale and a set of standardized descriptions of wet and contaminated condition") and validity of the performance model ("
… there may be instances where the model may not apply values conservative enough for TOA landing assessments.)
The FAA places greater reliance on PIREPs (PBAR) than EASA, Chapt 4.
There is extensive small print to fall foul of. e.g. "
Braking action reports should be based solely on the wheel braking component of the aircraft’s deceleration. Pilots need to understand that stopping results do not necessarily correlate to braking action. The effects of aerodynamic forces, while beneficial to stopping performance, should not be considered when making a braking action report. For turbojets, the effect of reverse thrust should not be considered. Likewise, for propeller driven airplanes, the effect of reverse pitch should not be considered."
and much more,
'Aircraft Landing Performance and Runway Excursions Mitigation'
https://www.faa.gov/documentLibrary/...91-79B_FAA.pdf
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