It happened before the security crackdowns of the post-9/11 era but the in-flight meltdown of two twin sisters remains one of the most-widely viewed examples of air rage caught on tape.

In April, 2001, a United Airlines flight headed to Shanghai, China had to be diverted to Anchorage, Alaska after sisters Crystal and Cynthia Mikula began fighting on the plane and cursing, screaming and spitting on other passengers. The crew stepped in but one flight attendant got punched in the nose.

The punch was thrown by Cynthia Mikula, who was later sentenced to five years' probation for disrupting the flight and fined more than $80,000. Crystal Mikula was sentenced to two years' probation and a $500 fine. Both were also ordered to perform more than 200 hours of community service.

At the time of the flight, the women said they were on their way to a modeling competition in Shanghai.

This week, "20/20? will show you the inside stories of the airline industry and air travel. The Mikula sisters, as you'll find out, aren't the only stars of videos showing outrageous scenes aboard an airplane.

WATCH "20/20? FRIDAY AT 10 P.M. ET and tweet #JustPlaneCrazy to share your air travel stories.