Originally Posted by LH2
[PBL:
perpendicular to the geodetic latitude]
Indeed it is according to your reference, which I've now looked up.
Just to clarify in case of misunderstanding: my answer addressed the question what is perpendicular to the reference ellipsoid, and I think the answer is standard, isn't it?
You point out that the accuracy of inertial navigation is dependent amongst other things upon the integrated effects of local gravity over the route of flight, not over some purely mathematical (engineering) construct such as the geodetic latitude. Indeed so, but I haven't worked in navigational avionics so have no idea of the magnitude of the difference between construct and reality, so in particular I can't comment on your numerical example.
Thanks for the references!
PBL