In the aviation industry, a flight number or flight designator is a code for an airline service consisting of a two-character airline designator and a 1 to 4 digit number.IATA Passenger Glossary of Terms (15 June 2018) [www.iata.org/whatwedo/passenger/.../IATA-Passenger-Glossary-of-Terms.xlsx] For example, QF9 is a Qantas Airways service from Perth, Australia to London Heathrow. A service is called "direct" if it is covered by a single flight number, regardless of the number of stops or equipment changes. For example, QF1 flies from Sydney to Singapore to London on Qantas Airways. A given flight segment may have multiple flight numbers on different airlines under a code-sharing agreement. Strictly speaking, the flight number is just the numerical part, but it is commonly used for the entire flight designator.
The flight designator of the operating carrier of a commercial flight is used as a call sign.ICAO, "Glossary" This is distinct from the aircraft's registration number, which identifies a specific airplane.
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.Peter Newell, "Flight Numbering Alternatives", Ascend: A Magazine for Airline Executives, issue 2, 2014 Eastbound and northbound flights are traditionally assigned 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 codeshare numbers for flights operated by different airlines or even railways.
Likewise, flight numbers larger than 9000 usually refer to 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, which initially used the first digit of the flight number to represent the location of the base (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 expansion 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 and Xiamen 8XXX, and stipulating that Chinese airlines should not use the same flight numbers with each other. However, this rule is no longer strictly enforced, as the allocated numbers have become shortage of use. As a result, there are three special cases in China: 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. 2. Flagship flights do not use one-digit or two-digit flight numbers, and may even be four-digit flight numbers. 3. Flight numbers in the event of an aviation accident will generally 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.
The lowest-numbered passenger flight starts at 101 for Air China and 100 for Cathay Pacific. CA 101 is a scheduled daily flight from PEK (Beijing Capital) to HKG (Hong Kong Intl') with an outbound flight of CA 102. Flight CX 100 departs from SYD (Sydney-Kingsford Smith) and arrives at HKG (Hong Kong Intl'). Most of Air China's international flights are numbered 101-999 with an exception of codeshare flights.
Codeshare
In a codeshare, airlines share their aircraft with others, resulting in the flight having more than one flight number on the same sector, and either the same or different flight numbers on joined sectors.
As an example, QF8412 flies from Dubai to Sydney, but it is codeshared with and operated as EK412. Another example is QF3920, which is a flight from Lima, Peru to Santiago, Chile that is also codeshared with LATAM 523.
List of lowest-numbered passenger flights by airlines Most flights are non-stop from A to B, and few are from A to B then to C (both A–B and B–C have flight number 1). Aircraft type may change due to operation need or unforeseen circumstance. Airline IATA Flight No ICAO Flight NoFromToThen to (if applicable)Aircraft TypeAeroméxicoAM1AMX1Boeing 787-8/787-9Air CanadaAC1ACA1Boeing 777-300ERAir Canada ExpressQK1 JZA1 Bombardier CRJ900Air ChinaCA101CCA101 Comac C919Air FranceAF1AFR1Boeing 777-200ER / 777-300ERAir JapanNQ1AJX1Boeing 787-8Air MacauNX1AMU1Airbus A321Air New ZealandNZ1ANZ1Boeing 787-9Air NiuginiPX1ANG1https://www.flightaware.com/live/flight/ANG1 Boeing 737-800Air Tahiti NuiTN1THT1Boeing 787-9Alaska AirlinesAS1ASA1Boeing 737-800American AirlinesAA1AAL1Airbus A321Cape Air9K1KAP1Cessna 402Delta Air LinesDL1DAL1Boeing 767-400EREl AlLY1ELY1Boeing 787-9EmiratesEK1UAE1Airbus A380-800Etihad AirwaysEY1ETD1Airbus A380-800 / Boeing 787-9FedEx ExpressFX1FDX1Boeing 777FFinnairAY1FIN1Airbus A350-900FlydubaiFZ1FDB1 Boeing 737-MAX 8Hawaiian AirlinesHA1HAL1Airbus A330-200Japan AirlinesJL1JAL1Boeing 777-300ERJapan Transocean AirNU1JTA1Boeing 737-800JetBlue AirwaysB61JBU1Airbus A321-200 / Airbus A320-200JetstarJQ1JST1Boeing 787-8Jin AirLJ1JNA1Boeing 737-800LATAM ChileLA1LAN1Airbus A320LOT Polish AirlinesLO1LOT1Boeing 787-8LufthansaLH1DLH1Airbus A321 / A320neoMalaysia AirlinesMH1MAS1Airbus A350-900Nauru AirlinesON1RON1Boeing 737-300QantasQF1QFA1Airbus A380-800Qatar AirwaysQR1QTR1Boeing 777-200LR / 777-300ER / Airbus A350-900Royal Brunei AirlinesBI1RBA1Boeing 787-8Scandinavian AirlinesSK1SAS1Airbus A320neoSkymark AirlinesBC1SKY1 FukuokaBoeing 737-800Southwest AirlinesWN1SWA1Boeing 737-700 / 737-800 / 737-MAX 8SpiceJetSG1SEJ1Boeing 737-800Spirit AirlinesNK1NKS1Airbus A321 / Airbus A321neoSpring JapanIJ1SJO1https://www.flightaware.com/live/flight/SJO1 Boeing 737-800Starlux AirlinesJX1SJX1 Taipei–TaoyuanAirbus A350-900Turkish AirlinesTK1THY1Boeing 777-300ERUnited AirlinesUA1UAL1Boeing 787-9WestJetWS1WJA1Boeing 787-9Zipair TokyoZG1TZP1Boeing 787-8
A notable former flight number 1 was British Airways flight BA1, operated by the Concorde between London Heathrow and New York's John F. Kennedy airport. After the retirement of Concorde in 2003, the flight number was retired with it, but in 2009 it was given to the all business class A318 flight between London City Airport and New York JFK via Shannon in Ireland. This route ceased operation in 2020 due to the COVID-19 pandemic, and British Airways has since announced it will not be restarting the service.
Flight number changes Flight numbers are often taken out of use after a crash or a serious incident. Examples include:
Following the disappearance of Malaysia Airlines Flight 370, the airline changed the flight number for subsequent flights following the same route to MH 318. After the crash of Air France Flight 447 over the Atlantic Ocean, a regular scheduled flight from Rio de Janeiro to Paris, the flight number was changed to AF 445. Following the crash of Asiana Airlines Flight 214 in July 2013, Asiana change the numbered flight pairs from Asiana Airlines 213/214 to 211/212. Following the crash of Air India Flight 171 in Ahmedabad in June 2025, Air India changed the Ahmedabad to London Gatwick flight number to AI 159. Sometimes, airlines change their flight numbers when the routes are changed. For example, United flights UA 801 and UA 802 were renumbered as UA 820 (LAX-HKG-BKK) and UA 821 (BKK-HKG-LAX) when the flights were extended. United Flights UA 153 (HKG-LAX) and UA 152 (LAX-HKG), however, retained the original flight numbers when the additional segment to/from SGN (Ho Chi Minh City, Vietnam) was added.
Flight number conservation Airline "mega-mergers", in markets such as the United States, have made it necessary to break conventional flight numbering schemes. Organizations such as IATA, ICAO, ARC, as well as CRS systems and the FAA's ATC systems limit flight numbers to four digits (0001 to 9999). The pool of available flight numbers has been outstripped by demand for them by emergent mega-carriers. As such, some carriers use the same flight number for back-and-forth flights (e.g., DCA-PBI-DCA), or in other cases carriers have assigned a single flight number to a multi-leg flight (e.g., ICT-DAL-HOU-MDW-OMA-DEN-ABQ-LAS-BDL).
Flight designator Although 'flight number' is the term used colloquially, the official term as defined in the Standard Schedules Information Manual (SSIM) published annually by the International Air Transport Association (IATA) Schedules Information Standards Committee (SISC), is flight designator. Officially the term 'flight number' refers to the numeric part (up to four digits) of a flight code. For example, in the flight codes QF103 and AF296Q, "103" and "296" are flight numbers. Even within the airline and airport industry, it is common to use the colloquial term rather than the official term.
Spacecraft Flight numbers are also sometimes used for spacecraft, though a flight number for an expendable rocket (such as Ariane 5 Flight 501) might more reasonably be called the serial number of the vehicle used, since an expendable rocket can only be launched once. Space Shuttle missions used numbers with the STS prefix, for example, STS-93. SpaceX uses sequential numbers for flights of reused boosters. As an example, Crew-2 used booster B1061.2 (the second flight of booster B1061).
See also Airline call sign Codeshare agreement Change of gauge (aviation)
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