John
With the greatest respect, that is the rule of thumb used for engine-out approaches when simulating a double engine failure.
The technique is to position approximately 15 miles out at 15,000 ft and plan your approach from there.
I appreciate that the L/D ratio at altitude exceeds this figure - the point being that you aren't going to glide with that performance all the way down.
The idea that you will glide with a L/D ratio approaching 1:20 to a landing is not feasible - unless you plan for a straight-in approach which, considering you're going to have to configure the aircraft and position for the landing, is unlikely.
It's what I've done several times in the sim - with a reputable airline - and it works out fine. I'm surprised no-one else has confirmed this as it's standard SOP for Boeing 737s?
Kind regards
FOK
