Plot hole: When the group is walking through the jungle for the 2nd time, they have nothing more than their backpacks and a horse to accompany them. Suddenly we see them rowing down a river on a boat and raft. After making peace with the savages, when they have to let a group member go to get medical help, they have been washed ashore as they have been traveling on a single raft since the canoe was damaged by spear attack. How is it that they had a horse and an Indian guide to send away with their injured man? (01:16:55)
Factual error: The way surveying is done is plain stupid. Percy Fawcett sets up a transit in the middle of a thick jungle, Henry Costin stands 10 feet in front of him holding the rod in one hand and a notepad in the other, then Percy looks through the transit and somehow reads the geographic coordinates out of thin air. This scene repeats couple of times during the movie.