A red-eye flight is a flight operated by an airline departing late at night and arriving early the next morning, typically between the period from 9:00 p.m. to 7:00 a.m. The term red-eye derives from the fatigue symptom of having red eyes, which can be caused by:
Dehydration from the low humidity environment of aircraft cabins
In the United States, Canada, and Australia, red-eye flights fly from the west to the east coast, capitalizing on the timezone changes and the rising sun. But the term can refer to any overnight flight which travels in the opposite direction of the Earth's rotation, i.e., east to west.
In addition to allowing passengers to have a full day at both the departure and destination city and travel by night, red-eye flights operate for the following reasons:
Repositioning aircraft and flight crew for the following day's schedule
Increasing the utilization of aircraft in a company's fleet
Providing additional service to lower cost markets
Allowing the airline to advertise lower fares to some destinations
In the 1930s and 1940s, red-eye flights were not possible, as most airports did not have the equipment necessary to work at night. There are still airports that do not function after certain hours, so red-eye flights can take off only from those airports that are operational after midnight.
