Editing Flight number (section)

==Conventions==
A number of conventions have been developed for defining flight numbers, although these vary widely from airline to airline, and are increasingly being modified.<ref>Peter Newell, "Flight Numbering Alternatives", ''Ascend: A Magazine for Airline Executives'', issue 2, 2014 [http://www.ascendforairlines.com/2014-issue-no-2/flight-numbering-alternatives]</ref> Eastbound and northbound flights are traditionally assigned [[Even and odd numbers|even numbers]], while westbound and southbound flights have odd numbers. Other airlines will use an odd number for an outbound flight and use the next even number for the reverse inbound flight.  For destinations served by multiple flights per day, numbers tend to increase during the day.  Hence, a flight from point A to point B might be flight 401 and the return flight from B to A would be 402, while the next pair of flights on the same route would usually be assigned codes 403 and 404.

Flight numbers of less than three digits are often assigned to long-haul or otherwise premium flights. For example, flight number 1 is often used for an airline's "flagship" service (see below for a 'List of flight number 1 by airlines'). However [[Cathay Pacific]] assigns flight numbers which are less than 100 for cargo flights.

Four-digit numbers in the range 3000 to 5999 typically represent regional affiliate flights, while numbers larger than 6000 are generally [[code sharing|codeshare]] numbers for flights operated by different airlines or even [[high-speed rail|railways]].

Likewise, flight numbers larger than 9000 usually refer to [[dead mileage|ferry flights]]; these carry no passengers and are used to relocate aircraft to or from a maintenance base, or from one air travel market to another in order to start new commercial flights. Flight numbers starting with 8 are often used for charter flights, but it always depends on the commercial carrier's choice.

===Flight numbering system in mainland China===
The People's Republic of China uses a completely different system for assigning flight segments than most countries; prior to 1988 reformation, there was only one major airline in mainland China, [[CAAC Airlines|CAAC]], which initially used “the first digit of the flight number represents the base airport (1 North China, 2 Northwest China, 3 South China, 4 Southwest China, 5 East China, and 6 Northeast China) for domestic flights, and the end of the number has an odd digit for departures and an even digit for return trips”. In the 1980s, a second digit joined, indicating the destination of flights (many domestic flights of [[Air China]] and [[China Eastern]] from their base still follow this rule); one-digit and two-digit flight numbers are usually reserved for executive charters or special mission flights (e.g., the flight carrying the black boxes and American investigators of the [[China Eastern Airlines Flight 5735]] in 2022 used flight numbers CA79 and CA80).
With the privatization and booming of China's civil aviation, in 2004 the CAAC issued a system for allocating flight numbers across the country, with [[Air China]] allocated 1XXX, 4XXX, and 9XX, [[China Eastern]] 2XXX and 5XXX, [[China Southern]] 3XXX and 6XXX, [[Hainan Airlines]] 7XXX, [[Sichuan Airlines|Sichuan]] and [[Xiamen Airlines|Xiamen]] 8XXX, and stipulating that Chinese airlines should not use the same flight numbers each other. However, this rule is no longer strictly enforced, as the allocated numbers have become shortage of use.<br>
As a result, there are three special cases in China:<br>
1. Flight number 9XXX may be a regular flight, while smaller number like 500 or 2000 might be used on ferry flights or [[codeshare]] ones.<br>
2. Flagship flights do not use one-digit or two-digit flight numbers, and may even be four-digit flight numbers.<br>
3. Flight numbers in the event of an aviation accident will not be retired, as seen on [[Air China Flight 129]] which is still active as of January 2025 (albeit using a different type of aircraft). Still, there are exceptions, as with the case of the aforementioned China Eastern Airlines Flight 5735.<!--As of 2025, Flight 5735 is no longer used by China Eastern-->