Re: Gliding Heavies
All jet aircraft descend from cruise altitude with the engines at idle thrust, initially.A rough indication of range in nautical miles to touchdown is given by multiplying the cruise height in thousands of feet by 3 (eg at 35000 feet, range is 35 X 3 = 105nm). In an ALL ENGINE-OUT condition, the only difference, at first, is the loss of flight-idle thrust. If the aircraft is then flown in the glide at the FMC engine-out descent speed, the X 3 rule is still fairly accurate. No extreme nose-down attitudes or high speeds are required. However, you need to allow a margin for manoueving when in the vicinity of a suitable airfield and should plan to be overhead, or abeam the field, at about 10,000ft agl. This effectively reduces the gliding range by about 30nm. Thus a B777 cruising at 35,000 could be expected to glide to and get into an airfield within approx 70-75nm (still air).
We used to practise the glide-to-land in the BA simulators, if time permitted, after the flame-out/relight scenario. However, it is not known if the simulator performance is valid in the no-engines condition, so the following is a guide only.
Below 10,000ft, a speed of about 230 kts seemed a good manoeuvre speed. This is close to best L/D and gives a reasonable radius of turn. At average weights, the wings level ROD was about 1500fm, up to 2500fm in a 30deg. banked turn. You can do the mathematics from there to plan an approach from the abeam or overhead.
With the aircraft (simulator) postioned at 8-10 miles out, in 'clean' configuration and on the 3 deg. G/S, it would descend at approx 1200fm and maintain the speed (this was in still air.) Within 5nm, the speed was reduced to a sensible value by use of gear,flap and speedbrake - this was when the finer judgement was required. Better to touch down at 200kts than than stall on the approach - lack of a 'go-round' option helps the concentration! With the APU and RAT powering electrics and hydraulics, in the B777, a perfectly good autoland could be made. An alternative technique was to cross the outer marker at twice the normal height, but at normal speed and configuration.This data may give a rough guide, but might not be anywhere near valid for YOUR aircraft.