Originally Posted by
Panic Stations
GrobDJ - I was speaking in laymans terms, as every pilot knows that trying to stretch the glide doesn't work and gets you beaten about the head by your first flying instructor. Were I faced with a total loss of thrust at 500ft, fully configured for landing, my first response would be to pitch down to maintain the speed at Vref and not stall the aircraft short of the runway. I would shortly after expect to be alerted by my colleagues screams that we were going to land very short and then reduce the speed back to the stick shaker if necessary to ensure I cleared any big hard objects in the distant undershoot (such as Hatton Cross tube station or the Jurys Inn hotel) before easing the speed back up if possible once assured of reaching something relatively flat. If the video on the BBC is of the aircraft in question it looks very much like what they were doing. The concept of Vmd doesn't really work in a dirty airliner, nobody really knows what it is and it's probably too late to get to it anyway.
Apologies for gate-crashing your forum last night whilst pPrune was down, thanks to Rambuster for making me welcome, and well, without PanicStations sounding off there'd be little to talk about!
Speculation, argument and debate are all parts of the healthy way in which aviation exorcises its demons, making it the safest technology on the planet.
I'm not a professional pilot, so forgive me if the following turns out to be a load of rubbish, however I do think Vmd is pertinent to gliding whatever the aircraft configuration. I agree, Vmd is a speed usually pertaining to the 'clean' configuration, but there will be a minimum drag speed for each flap setting and these speeds will be achieved at less than maximum angle of attack (i.e lower the nose, increase speed). Vmd is the speed at which the ratio between lift and drag is highest (L/D ratio), and the glide will be the furthest achievable without power.
No doubt those with access to 777 simulators will be re-running the flight as we speak.
These are very rough assumptions:
Let's suppose BA38 lost all thrust at 1 mile(1850m) from the threshold, height 100m; given that it fell short by 350m, it might make the threshold if L/D could be increased by 20% (350/1850) over the final phase of flight. If drag could be reduced by 5%, and lift were increased by 15% 1.15/0.95=1.21, that should do the trick. But lift increases with the square of speed so about 7% extra speed will generate the extra lift required.
BA38 looks to have landed with a high flap setting.
Is there a case for reducing flap and increasing speed immediately when suffering an engine failure on final approach when plenty of runway is available to counter the higher landing speed? Max thrust on the remaining engine increases the possibility of a double engine failure. Or the plane may be out of fuel, so the other engine is about to pack up too. Does the 777 engine failure procedure ready the pilots for a second failure shortly after? (oops I shut down the wrong one?)
Or is it the case that the higher landing speed presents a greater hazard to the safety of the flight?