Factual error: When the aircraft crashes on the island, the front of the aircraft strikes the ground which would have bent the propeller. They would have never been able to fly it again with that prop.
Factual error: Ford and Heche are supposedly on an island in the middle of nowhere, but in some shots you can see the tall buildings of a city off in the distance.
Factual error: As Robin and her fiancee are heading off to Macatea, there is a quick shot of an Aloha Airlines plane as it is landing. Aloha Airlines does not operate there or anywhere near there, but the movie was filmed in Hawaii so they apparently used what they had.
Lynette Carrington
Answer: Once they were in the air, Quinn would be able to navigate by sight. He was an experienced pilot and and was familiar with the territory and the different islands' configurations. He would also be looking for ship traffic, and he had a general idea which of several islands they were on. Once in the air, he would easily know which direction he was heading based on the position of the sun.
raywestBut he passed out. And the ocean is a big expanse, not a lot of landmarks to navigate by.