i tried to compile my own answer to the problem presented by SFLY and when searching for B77 stall speed numbers i have found all the answers already there.
an executive summary:
FullWings: I think this discussion shows that you can't write SOPs for every conceivable occurrence and that
Airmanship is thankfully still alive and well in some quarters.
some formal source to consider:
Boeing 744 QRH: Procedures Beyond the Scope of the QRH
Introduction:
It is rare to encounter inflight events which are beyond the scope of
established non-normal procedures. These events can arise as a result of
unusual occurrences such as a mid-air collision, bomb explosion or other
major malfunction. In these situations the flight crew may be required to
accomplish multiple non-normal checklists, selected elements of several
different checklists (applied as necessary to fit the situation) or find little
or no specific guidance and need to rely on their own judgement and
experience. Because of the highly infrequent nature of these occurrences,
it is not practical or possible to create definitive flight crew procedures to
cover all events. (the bolding is mine)
short thread just on the same subject can be found here
http://www.pprune.org/tech-log/30928...st3852210.html
SFLY's problem was also discussed after
D O Guerrero asked
http://www.pprune.org/rumours-news/3...ll#post3845436
how does landing at very low speed or at the stall speed increase the glide? I thought the maximum glide distance would be achieved at best glide speed which is presumably quite a lot greater than the stall speed on a 777? And therefore that any speed either greater or lesser would only have the effect of reducing the glide distance. I don't dispute that the crew would have wanted to slow the aircraft as much as possible just prior to touching down - but I would have thought that slowing to stall speed in order to try and make the perimeter would be an extraordinarily bad idea....
and got the answers among others from
Mad (Flt) Scientist:
You are correct that best glide speed is not stall speed, and an indefinite glide is best achieved at best glide speed.
However, gliding involves exchanging potential energy for kinetic energy (or, using a gravity component along the flight path to combat drag). If you were trying to extend a glide, and were, say, 500ft AGL, at say 1.3vs, you might be better off trying to use up some of the stored KE represented by the speed rather than simply use up that 500ft. Exactly what the best energy management would be is dependent on a lot of aircraft dependent factors, but hitting the ground at your lowest possible flying speed does ensure there was no wasted energy left which might have been used to extend the glide.
eyeinthesky:
Aircraft approach at a speed which gives them a margin above the stall speed (usually around 30% higher). In an emergency such as this, this 30% extra speed can be traded for height and therefore 'stretch' the flight path compared to that which would result from flying 30% above Vs with no power. It is a measure which has only a limited life, since once the stall speed is close the nose must be lowered again to prevent the stall. Then the aircraft is committed to where it will end up. It needs fine judgement and the failure to occur not before a certain point for it to work and the aircraft to reach the field. it would appear that in this case it worked, so well done to the teams aboard!
Unfortunately, there are too many crash sites in history where an attempt to 'stretch the glide' had insufficient energy (potential or kinetic) for it to work and the result was a wreck.
and
moosp:
A colleague of mine flew several profiles on the 777-200 sim this morning (the real one, please, not the MS version) failing various engines at 500 and 300 ft on the LHR 27L model. A failure of 2 engines between 500 and 300 feet, with an attempt to stretch the glide towards stall speed produced a touchdown at a similar point on the visual model as the BA aircraft.