Well, if the pilot rotated at Vr at a rate of one degree per second, he or she would have chewed up a lot f runway before the wheels lifted compared to a normal flight where the rotation rate is approx 2.5 degrees per second.
Rough figures, at 150kts you're using 250ft of runway a second.
The aircraft leaves the ground at about 11 degrees nose up.
At the normal rotation rate it is 4.4 seconds from beginning the rotation until airborne.
At 1 degree per sec it is 11 seconds.
That's an extra 6.6 seconds on the ground with the slower rate.
6.6 seconds = approx 1600ft of extra runway used.
Kinda explains everything really ( assuming the estimated rotation rate is correct).
Edit; I just had a look in the FCOM and lift off at flap 5 is 8 degrees, not 11, so the slower rate uses an extra 1200ft of runway, not 1600ft.
Last edited by framer; 20th Oct 2017 at 06:27.