Originally Posted by LOKE
I alway used:
2nm/1000 @ high speed
2.5nm/1000 @ 250
3nm @ close to L/D
Of course weight had a substantial impact and naturally wind had to be considered.
We glider pilots are intimately acquainted with best L/D, though not for Boeings. Weight doesn't change the best L/D, but it does change the speed at which the best L/D is achieved - the heavier you are, the faster you need to fly to be at best L/D.
3 nm per 1000 ft = 18:1, which seems about right from other things I've read.
For greatest distance across the ground you should fly a little slower (between best L/D and min sink) in a tailwind, and somewhat faster in a headwind. The headwind calculations require information about the gliding polar, but a good rule of thumb in gliders is that you achieve the greatest ground distance into a headwind at best L/D plus half headwind. At Boeing glide speeds, if the rule scales up, that might be very little difference.
The Gimli glider, a Boeing 767, apparently achieved only 12:1 (but maybe didn't need to fly best L/D). It helped that the captain was also a glider pilot.
http://en.wikipedia.org/wiki/Gimli_Glider