Originally Posted by
Rod Eddington
...having CPT-POMAX-BRI-procedural ILS will have a lot more track miles than you can actually expect and hence a rubbish descent profile, as 99 times out of 100 you will get something that approximates to CPT-POMAX-CF27.
That's sensible enough for me (99 times out of 100
), Rod, and thanks for the answer, and for taking my question seriously. I had wondered whether it was due to computed descent profile reasons, so it's nice to have that confirmed. I can understand why you'd want to do it this way round... pax don't like that recomputed 'semi-dive', if done the other way around, I can well understand!
Of course, I can't help wondering now why on earth the FMC cannot use its loaf a bit more, and determine the 'end of route' status more effectively. After all, it knows the field elevation, so one would've thought it could determine that if you're greater than 622 feet on the altimeter, your journey is not strictly complete yet! It is unlikely that your QNH will be more than a couple of hundred feet out at the absolute worst (and probably, a
lot more accurate than that) - so 'pressure-setting reasons' don't really provide a tenable reason for not doing this, I feel.
Similarly, one would've thought that 'weight-on-wheels' would be another useful check-and-balance for determining true arrival - assuming the FMC can do that (which I believe it can, in order to provide you with groundspeed readings on the gear ECAM when taxying).
I guess that's one for whoever it is that writes the software for the FMC, really, though! Maybe there's another technical reason why this is difficult to fix, but on the face of it, calling 'end of route' simply on the basis of a lat-lon position and no remaining FMC waypoints before the field position, would seem, er, a tad slack, no?
Thanks again, Rod, much appreciated.