Other mistake: When the Vikings are chasing the main characters in the boats, the Vikings' ship isn't moving although they are still rowing.
The Island at the Top of the World (1974)
1 other mistake
Directed by: Robert Stevenson
Starring: Mako, David Hartman, Donald Sinden, Jacques Marin
Factual error: As the airship approaches Astragard it's headed due North; yet the distant clouds are backlit by the Sun. The Sun should be to the South.