chr, the commercial factors 1.67/1.92 are requirements for dispatch and are based on AFM distances. The unfactored AFM distances are not realistically achievable in operation.
EASA requires an assessment of the ‘conditions’ before landing so that the expected distance will be safe (EU OPS1.400). Some operators use the fully factored AFM distances, updated for actual arrival conditions; this should provide an equivalent level of safety as for dispatch.
Some, most, manufacturers provide advisory landing data (QRH/FCOM), which may be based on the unfactored AFM distance or similar calculations. These are unlikely to be the same as the AFM – 1000ft touchdown point, use of reverse, etc, but the unfactored distances may be achievable in operation (emergency use), but the assumptions in the calculations should be carefully studied.
EU OPS requires a
minimum additive of 15% above distance calculated – as factored and increased by EU OPS 1.515, 1.520. These distances represent a more realistic value for pilots to achieve with a safety margin, however as noted in FAA SAFO15009 these distances may still be insufficient in some wet conditions.
Although private operations may not be governed by the same regulations as commercial, they will at some point be answerable to a requirement to operate safely. Thus it might be judged that the use of unfactored distances would not meet the minimum safety requirements in aviation.
Book figures are fine if you understand the basis of the book, the factors, the safety margins, and the assumptions made about flight technique (as per #3).
Unfortunately the book doesn’t know when the pilot is going to have a bad day, or the tailwind is stronger than reported or the runway more slippery, … ….
Managing Threats and Errors During Approach and Landing