I'd say that
Eagles to
Mordor is above
Balrog wings. One of them is a "plot-hole" and the other is just something we don't know.
My guess is that the error in thinking derives from the scene where Eagles arrive at Mount Doom to save
Frodo and
Sam, so why wouldn't hey have been able to ...
HUGE difference.
When the Eagles arrived at Mount Doom to rescue Frodo and Sam,
the One Ring had been destroyed,
Sauron had been permanently de-bodied and rendered impotent,
Barad-dûr had fallen into utter ruin, Sauron's forces at the Black gates were destroyed or fleeing, and the plain of Mordor,
Gorgoroth, was absolutely deserted of any troops, all of which had been sent to the
Black Gate. Compare that to the scene in RoTK, Book Six, chapter II "The Land of Shadow", where Frodo and Sam scrambled up the inner, lower mountain range in western Mordor:
"Frodo and Sam gazed out in mingled loathing and wonder on this hateful land. Between them and the smoking mountain, and about it north and south, all seemed ruinous and dead, a desert burned and choked. They wondered how the Lord of this
realm maintained and fed his slaves and his
armies. Yet armies he had. As far as their eyes could reach, along the skirts of the Morgai and away southward, there were camps, some of tents, some ordered like small towns. One of the largest of these was right below them. Barely a mile out into the plain it clustered like some huge nest of insects, with straight dreary streets of huts and long low drab
buildings. About it the ground was busy with folk going to and fro; a wide road ran from it south-east to join the Morgul-way, and along it many lines of small black shapes were hurrying."
This was, according to Appendix B, on 16 March 3019 (
SR 1419), nine days before the destruction of the One Ring.
When could, at the earliest, the decision to "draft" the Eagles to their "air-freight" assignment have been taken?
At the
Council of Elrond on 25 October 3018 (SR 1418). So "Eagle airlines" would have taken off on 26 October? Erm, no way.
There have been enough posts about the Eagles, similar to the
Ents, not being on anybody's side (definitely
not on Sauron's, but ...) as nobody was exactly on
their side, either. So, how do you contact the "
travel agent" for "Eagle airlines"?
Then the distance. On Karen Wynn Fonstad's only
map with a scale that shows both
Rivendell and Mordor, the distance in a straight line seems to be about 726 miles, or 1,169 kilometers. A cross-check with my copy of Christopher's map in my 2002 hardcover edition of FoTR yields about 717 miles, or 1,154 kilometers.
As I've mentioned above (on page 2 of this thread), in contrast to large migratory
birds like ducks, geese and swans, eagles aren't the greatest straight-line continuous fliers. They very much prefer to soar upwards on updrafts of any sort to continuously flapping their huge wings. So how long would they have needed for that distance?
And whom would they have transported? Only Frodo? I personally think not. At least
Gandalf, with whom the Eagles had a special relationship indirectly through
Radagast, and directly through an incident of his helping the King (Lord?) of the eagles recover from an
arrow wound as described in "The
Hobbit" would be necessary. A lot of that flight would have been over enemy territory, and there's always the issue of the
Nazgûl on their winged
fell beasts.
No, there is no "plot-hole", as far as I can see.