Blue Hauler
Ahhh now that's another story altogether and revolves around a certification philosophy, known as FAR Part 25 Transport Category which just happens to apply to all aircraft >= 5700kgs.
Landing is the least accurate of all our pitiful fumblings around in the manner of piloting a heavier than air machine..
So they apply a cuppla std deviations (67%) to the figures that are derived by everything happening exactly as it should to allow for that.
That is, if you use the factored number you have got your arse statistically covered for just about every reasonable combination of events not happening exactly as planned.
It is to do with giving the fare paying passenger an even break.
Thers a fair bit more to it but that'll do for the moment, I'm off to bed.