Landing Performance
Hello PPRuNers, this should be a quick one!
I'm having trouble understanding the difference between theory and reality of a landing, as per FAR 25 requirements go.
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.
Now, the reality practical day to day technique that I see, and I just read a 737 FCTM to don't get the technique wrong, is that, this is not what happens.
Generally, the aircraft comes on a 3º glidepath (let's assume an ILS glideslope for being precise), and at landing configuration, descends at Vap (not Vref, more so if you're on autothrottle or the like) until you're about 30ft of height, initiate the flare, which should be no more than 2º - 3º of pitch, and ideally you retard the thrust levers and they should reach idle when you finish the flare, and just wait for the plane to touchdown.
So I'm having trouble understanding, if you use Vap all the way down until you retard the levers, you're not crossing 50ft at Vref, and in a 3º glideslope/path that directs you to the 1000ft mark, the only way of touching down in it is with an almost hard landing, since you're in a +- 700ft/min descent rate established on the glideslope. If you don't want to deviate from the glideslope, nor some EGPWS glideslope warning, you need to maintain it, and when initiating the flare, you will arrest the descent rate enough for the aircraft to touchdown at least some distance far from the 1000ft mark.
What I see used 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. But by doing that, they're deviating from the glideslope, and it seems to be the so called 'dive down' that we must not do. On very short runways they aim at the 500ft marking, striving to touchdown at the first inch of the 1000ft mark.
So, my guess is, for certification, the test pilot generally crashlands the plane at a high vertical velocity to demonstrate the stopping distance and that it didn't fell off to pieces, or I'm missing something very important, which is the reason for this post.
So, blast away your views, and thank you in advance!