These sort of questions come up regularly and are good for discussion. Unfortunately, we appear still to have some very adventurous folk out there in non-sked land.
The aircraft is certified for crossing the runway threshold at 50ft, at Vref, on a 3º slope, and to TOUCHDOWN the main landing gear at the 1000ft markings (the aiming point markings), and then comes the 60% of the dry runway distance.
Better to think along the following lines ..
(a) the certification flght test work confirms aerodynamic model predictions and provides the final model for developing AFM performance scheduling data.
(b) the presumption is that the aircraft will pass through a nominal 50ft screen height at a speed and on a slope suitable for the Type. The AFM will contain a description of the technique inherent in the AFM figures.
(c) touchdown cannot be at the aiming point for the reasons indicated by Mutt for a stable approach and must be somewhat further in.
(d) ducking under in the final approach phase is stupid in the extreme as it deliberately introduces a destabilisation into the approach at a critical stage .. plus .. it's not nice to drag the boundary fence wires into the touchdown zone.
(e) the TP will be doing his/her best to get "good" marketing data and will direct "not so good" runs to be discarded
(f) the aerodynamicists analysing the data set will, likewise, discard a few which "aren't quite nice"
(g) end result is that the TP cannot routinely and absolutely achieve the AFM basic data ... keeping in mind that the TP's technique will be a tad more savage than what one sees on the line .. the line pilot has no chance of doing so. It is just as well that we rarely see ourselves faced with seriously minimum runway lengths in the order of unfactored distances.
(h) he/she who routinely tries to achieve basic unfactored distances derived from AFM data .. is stupid and culpable .. no other word for it.
(i) now, whether one "needs" the full Part 25 factors is a moot point but they have stood the test of quite some time. However, one does need some pad to provide a reasonable probability of stopping on the seal.
(j) have an overrun without the factors and you might have some difficult explaining to do at the enquiry and in court during the actions for damages.
in practice is, that around 200ft of height, pilots generally start to aim between the 500ft and 1000ft runway markings, so that when they flare, they 'float' only enough to touchdown at the 1000ft mark.
That's called ducking under and is not sensible in the extreme, especially in other than very good met conditions.
for certification, the test pilot generally crashlands the plane at a high vertical velocity
Not reallly the case .. the TP endeavours to get the aircraft onto the ground in a reasonably repeatable fashion while not exceeding the structural limit descent rate and seeking to achieve the minimum total distance.
Vapp vs Vref is for wind component correction
The AFM will prescribe a technique which usually includes a small margin above the minimum Vref for nil wind conditions. In conditions of steady and gusty winds, additional margins will be prescribed with the intention of trading off some of the factor pad to improve final approach safety
so adding some airspeed to the vref will not make you go faster in regards to groundspeed when you have a head wind.
But keep in mind that the distance required is based on 50% of that headwind so your argument is a bit full of holes.
when it comes to flare you should aim for a smooth touchdown
I suggest that the aim is NOT for a smooth touchdown but, rather, a firm touchdown consistent with minimising the flare distance. Indeed a very smooth touchdown is not a good practice as it generally involves needless float .. although it is very pleasing to one's ego.
Sometimes one gets a touchdown so smooth that one isn't able to determine just where the touchdown occurs .. no sound, no vibration associated with the touchdown. I've only had this happen twice and both occasions were very unpleasant .. especially in the 722 where I knew that, if I were still in the air, .. everyone was going to know all about it in the next few seconds. Mind you, when the girls asked "who did that ?" after the flight .. I was only too modestly willing to take all the (quite unjustified) credit for it.
The requirements you rever to are for dispatch purposes. .. Quit arbitrary taken, hence the 60% factor.
I suggest that that is a foolish view to take. The driver for routine landing command decisions should be probability of a safe landing and eating significantly into the certification factors is not the best way to achieve that desire.
there is no requirement to land within 60% of the runway length
but one had better have a very good reason not to have done so if it all turns to custard ... noting that there is no requirement to achieve the landing within that distance .. only that the factor should be present .. the actual landing is expected to end up somewhere within the pad section of the scheduled distance.
only to accomplish a save landing.
.. and just how do you propose to do that in a reliable and predictable manner if you abandon your distance factors ?