Aerophobia, or fear of flying, is a relatively common phobia. Combine that with Triskaidekaphobia (the fear of the number 13) and Hexakosioihexekontahexaphobia (the fear of the number 666) and you have one anxiety-filled flight.

It's not likely that there were many superstitious passengers on Friday's Finnair flight #AY666 to Helsinki. Especially considering the flight from Copenhagen was headed to HEL. That's the airport code for Helsinki.

But Friday the 13th's flight #666 to HEL was mostly full today. This year the flight actually falls on a Friday the 13th twice. So those who believe such superstitions are silly fears based on old wives' tails or urban legends they can try pressing their luck again.

Ever wonder where the fear of the number 13 originated? Some believe it has biblical origins, "There are 12 hours, 12 months and in Christianity 12 apostles and this is a divine number. Add one more and it brings in a certain element of chaos,"  said Ulo Valk, professor of comparative folklore at the University of Tartu in Estonia.