1) Altitude to lose x 3 gives distance to descend
ie 30,000' to lose 30 x 3 = 90 miles + 10 as above = 100 miles
2) Ground speed x 5 gives ROD to give a 3deg descent
ie 300kts GS 300 x 5 = 1500'/min
3) Also, distance out x 3 gives height (x100') above level off point or runway if on 3 deg descent/glideslope
ie 20 miles before level off point
20 x 3 = 6000'
or if on glideslope
8 x 3 = 2400'
4 x 3 = 1200'
