hello tad,
top of descent = alt x3 in nm.
+10nm for deceleration from 300kias to 250kias to 210kias
for b738ng
er ton above/below 60ton(maxlanding wt = 65.3ton) : +/- 1 nm
for average wind correction
er 10 kts : +/- 2 nm tailwind/headwind.
during descent : groundspeed divided by 2 = rate of descent in ft/min for a 3°/5% glide path.
kind regards, sorry, can't get rid of the 2 smileys,
bm