A red-eye flight is any flight departing late at night and arriving early the next morning. The term red-eye derives from the fatigue symptom of having red eyes, which can be caused or aggravated by late-night travel.
A red-eye flight typically moves east during the night hours. It departs late at night, lasts only about three to five hours, an insufficient period to get fully rested in flight, and due to forward time zone changes the aircraft lands around dawn. As a result, many travelers are unable to get sufficiently rested before a new day of activity. From a marketing standpoint, the flights allow business travelers an opportunity to migrate eastward without having an impact on a full business day.
Most eastward transatlantic crossings from North America to Europe are operated overnight, but are generally not viewed as red-eye flights since they depart early in the evening and last at least seven hours. A full night's rest is theoretically possible as this is close to the seven to nine hours of nightly sleep recommended by the US National Sleep Foundation.
- Asia. All Nippon Airways and Japan Airlines used to operate red-eye flights from Hong Kong to Tokyo's Haneda, but they have changed to daytime flights. For Japanese red-eye flights, Cathay Pacific operates one each to Tokyo Narita and Osaka. Asiana, Korean Air as well as Cathay Pacific operate red-eye flights from Hong Kong to Seoul as well as Busan by Asiana and Dragonair. Cathay Pacific also operates such flights from Hong Kong to Oceania countries (Australia and New Zealand) and recently to Singapore and Kuala Lumpur, while have red-eye service from Jakarta to Hong Kong, and many flights from South-east Asia to Japan and Korea. All depart during evenings or around midnights, and land at the destinations in the early morning. Flights that leave India and Southwest Asia at night between 11 P.M. and 1 A.M. arrive in Singapore, Bangkok, and Kuala Lumpur between 5 A.M. and 8:30 A.M. Philippine Airlines also operates red-eye flights from Singapore and Bangkok back to Manila, which also have regular late-night flights from Manila to Seoul along with Korean Air and Asiana Airlines. In addition, both Asiana's and Korean Air's return flights from Kota Kinabalu depart at around midnight Malaysian time and arrive at Seoul by 7 A.M. Korean time for the convenience of Malaysian tourists, who are then able to commence sightseeing immediately. In addition, Japanese and Korean air carriers always have flights from Kuala Lumpur, Bangkok and Singapore to Japan and Korea.
- Australia. The majority of transcontinental flights are operated during the day, but as of 2010 red-eye flights operate from Perth to Sydney, Brisbane, Cairns, Canberra and Melbourne, and from Darwin to Sydney, Brisbane and Melbourne. Red-eye flights have previously operated from Australia to New Zealand and Fiji. Red-eye flights to Australia operate from various locations in South-East Asia.
- Brazil. TAM Airlines and Gol Transportes Aéreos both offer red-eye flights, called Big Owl (Portuguese: Corujão) flights in Brazil, with over 50 different routes throughout Brazil, all departing between 10 pm and 6 am.
- Europe. A few overnight flights from Europe to the Middle East and to Russia were being operated in 2009, all of which had a flight time of 3-6 hours and departed in mid-evening, arriving around dawn the next day. In 2012, multiple travel agencies offer budget night flights from the Canary Islands to the mainland of Europe, also generally having a 3-6 hour flight time.
- Russia. Russian airlines operate similar to U.S. airlines by connecting Moscow to Yakutsk, Irkutsk and Vladivostok with overnight red-eye flights. Russian transcontinental flights only last 5-8 hours but due to the northerly latitude the flights can cross as many as 8 time zones during this interval, drastically shortening the overnight experience. The flights depart Moscow around 6 pm and arrive at the eastern cities around 6 am the next day. One of the current examples of red-eye flight is Aeroflot's SU783 from Moscow to Magadan, departing 23:05 Moscow time and arriving 15:00 Magadan time on next day (flight time is 8 hours).
- United States and Canada. Red-eye flights connect West Coast cities to Central and East Coast cities. These typically depart the west coast around 10pm to midnight local, have a flight time of 3–5 hours but lose 2-3 hours due to time zone changes, and arrive around 5 am-7am. Red-eye flights also connect Hawaii and Alaska with West Coast mainland cities. Furthermore, red-eyes also connect Honolulu with Tokyo, as the flights only depart at night, and arrive around 6 to 7 hours later. 
Other meanings 
The term can refer to any overnight flight which travels in the direction similar to Earth's rotation (i.e. eastwards). The term may also be used to refer to many long-distance international flights which are long, even though the aircraft may never travel through a time zone that is in darkness.
Historical availability 
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, or have curfews for noise reasons, limiting the number of airports from which red-eye flights can depart.
- Gol pede autorização permanente para operar vôo noturno Folha Online. Retrieved on April 07, 2009.
- TAM lança ofertas corujão a partir de R$ 79,50 Rotas e Trilhas. Retrieved on April 07, 2009.