If I may amplify the previous post a bit.
DCA-speak to reflect what the AFM analyses do (ah, fond memories of previous lives) -
(a) gross to net infers a fudge factor reduction in performances for mum and the kids
(b) for climb this is easy - x% gross (nominal actual real world gradient) degrades by y% (per certification Standard) to give you z% (net for the calculations)
(c) does it not make sense, then, to do something similar for the third segment - climb gradient reflects excess thrust from which we can play with a gradient penalty reduction - this can be converted to a similar penalty in the acceleration capability for level flight (rather than climb gradient).
(d) as a result, the gross third segment to accelerate from V2 to the final climb speed, while reconfiguring from takeoff to final climb (x metres) will degrade to a longer distance (y metres) reflecting the lesser acceleration and longer time taken to get from V2 to final climb speed.
how can the horizontal distance to accelerate in the level segment be determined at all?
.. basic (mathematical) mechanics.
Acceleration as a function of time is integrated to give speed (strictly, velocity) as a function of time which, in turn, is integrated to give distance (gone) as a function of time and this ends up in the AFM charts - backroom stuff done by the aerodynamicists using performance models for the Type verified (and tweaked) using real world flight test data.
How could that distance (if able to be determined) be reduced by an allowance based on a climb gradient reduction from gross to net -a "reduction equivalent"
The gross to net reduction in climb gradient can be recalculated as a gross to net equivalent acceleration capability. Plug the revised acceleration capability into the integrating exercise et, voilą, you end up with a degraded (ie longer) distance reflecting the reduced acceleration capability.
if in fact that is what it means
exactly what it means ...
Main thing to recall - in years gone by, the DCA engineers (IT, RF, et al) had to put the local certification stuff in the ANOs (now CAOs). These were the 101 series and, for heavies, we were looking at 101.5 (UK Types) or 101.6 (US Types). The flying operations folk (who were good pilots but not so good at engineering) then recast the certification stuff into operational requirements (20 series) and got lots wrong in the translation.
Main thing - don't sweat it too much - the AFM does it all for you - you just have to apply the AFM requirements.
Confused I am.
That's why we have PPRuNe to sort out the confusion - what could be simpler ?
When looking at the bit of the profile that relates to the acceleration segment you must equally add a margin, in this case by adding distance
Yes and no.
Yes for the certification - it's built into the AFM.
No for the pilot - else you would be double dipping and the accountants would be after your neck. In any case the calculations are not intended for pilots to worry about.