The way I understand it is that is that the IAF for the intended airport and the FAF for the unintended airport are coincident (on an RNAV approach). The 4000 foot crossing restriction over the IAF put them way below a 3 degree GS for the intended airport, but put them basically on the GS for the unintended airport. They break out and have a runway in front of them with good PAPI indication. The crew transitions to the PAPIs and the rest is history. What the FMS is doing at this point is conjecture, and I will leave it to those more knowledgeable in the specific systems. Is it possible that if WITBA was coded or entered at 4000 in the FMS their vertical deviation indicator on the Primary Flight Display would have shown them on the correct profile at that point?
Last edited by acroguy; 23rd Nov 2013 at 01:18.