In the sim we did a deadstick autoland from 13 miles out, 6000ft and 250kt. It tracked the 3deg ILS all the way down, we just dropped flaps and gear on the speed schedule. It has a max landing weight in the region of 195 tons, yet the Vref at this weight is less than a 737. It has superbly efficient wings, & is very slippery for a big beast.
No doubt the 777 has efficient aerodynamics, but as I am sure you're all too well aware that as ATC we're rather limited against allowing you to fly at 6000 feet to capture an ILS at 13D, and you'll probably be back at 180kts or thereabouts. In fact, if I have any pilot close to 3000' at 10 miles, they're asking for further descent, so I am not sure this is a relevant example.
Now, I also have a question - from 13D, the 3 degree glide you state your sim tracked all the way down would still have you around 1866' AGL at the threshold (13Nm x 318' per mile descent = 4134 feet of descent). I take it you didn't track the glide at all, just happened to intercept it at around the TDZ, so meaning in this case the 777 DID NOT maintain a 3 degree slope with a double engine failure (which, in this accident, was not what happened anyway). In fact, 6000' in 13 miles is nearer 4.4 degrees (tan-1 461'/6076). The point I am trying to make here is that in the example you gave, using your figures, it was not a 3 degree path that was followed, and in a real world example where you are lower and slower (3000 AGL and 180kts or less, and just about to intercept the glideslope), I doubt the 777 could maintain a power off 3 degree glide.
Finally, correct me if I am wrong (I left engineering without 777 experience), but in every other type I have known, for an autoland, the buses need to be separated, which means 2 independant forms of power. In a twinjet, I would take this to mean a "deadstick autoland" is not possible?
The last point I'd make is that the a 737 at 195 tons would, no doubt have a very high Vref, but I guess Boeing haven't stretched it this far yet?
