Best dual engine failure best glides speeds SWAGS(Scientific, Wild *ss Guesses)
757/767 - Vref 30 + 90
737 - Vref 15 + 60
Perfect? No. Sometimes 'good enough' is just right until you get the checklist(if you have time).
Do we really need to guess when in a hurry?
From the very beginning of flight training "airspeed" is drummed into us, so perhaps we should be forgiven for having developed into a breed that seems to place so much emphasis on this one data input that is absolutely meaningless when considered on its own. We use reams of charts presenting us with PA, OAT and Weights to determine "speeds" that in reality correspond to an "angle of attack," the value of which is displayed on what I am sure is one of the least used and least understood instruments on a flight deck. As I don't fly either the 777 or A320, I have no idea if they are even fitted with an AOA indicator, but I'll bet few posters have received the benefit of much, if any, instruction on the use of this valuable little dial. I certainly hadn't, until I was fortunate to meet an instructor who knew more than a little bit about how the AOA indicator could help me. For a given aircraft type (and config) the AOA indicator will guide one swiftly to fly at the correct corresponding "speed" for a variety of flight regimes, irrespective of the WAT. Vref and V2 are perhaps the easiest examples to quote as we all know the values to look for; and further the configs are of no relavence (for these two examples). Similarly, in crusing flight (gear and flaps retracted), if one knows the angle of attack values for a given aircraft, calculations are of secondary priority when "speeds" for drift down, holding and even more importantly best glide (for max range in still air) may be needed in a hurry. Even during more leisurely moments, when perhaps ATC might ask if we can make another 2000 feet up, this magic little dial can guide us to an answer in an instant. I am not suggesting for one moment that the BA777 crew should or could have done anything at all different to change the outcome, in fact I congratulate and admire them for doing exactly what they did, especially the flap reduction. Knowing any AOA values for the config they were in at the time, and with the height available would not, I suspect, have made any difference to the outcome.
I am however sure that the outcome of at least twoother major hull losses could have been prevented if the crew had been able to make use of an AOA indicator, if indeed fitted, to either the Birgenair 301that departed with blocked pitot tubes, or the Aero Peru 603 with taped up static vents. (both Boeing 757's).