What happens when airlines around the world run out of flight numbers?

Numbers go on forever. But flight numbers are not. We have some unforgettable flight numbers, such as MH370, linked to the extraordinary disappearance of a Malaysian Airlines flight, or BA001, which British Airways used for its Concorde services. Some numbers, such as 13 or 666, have a tacit agreement not to be used for flights.

The flight numbers are also not too long. It would be impossible to find someone who has seen a flight number longer than four digits. Even within the existing four-digit maximum limit for flights, some numbers (generally those above 9000) are reserved for ferry flights, while others are used for codeshare flights.

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The lower the route number, the more important the flight is for the airline.

As airlines offer more flights every day, one has to ask whether airlines will eventually run out of flight numbers. And if so, what solutions are there?

Photo: Jonathan E. Hendry | Easy Flying

Airlines are actually on the verge of shutting down flights

Nearly half a decade ago, Indian aviation authorities were concerned that the growth of air traffic in the country and the resulting lack of flight numbers was a serious problem that needed to be investigated. The Times of India reported on the possibility of a looming safety problem due to the three-digit codes used on flights in India:

“The existing three-digit codes are causing increasing confusion and there have been a spate of safety concerns when similar sounding flight numbers operate from or to the same airport at approximately the same time – which is becoming increasingly common due to traffic volumes.”

Photo: Leonard Zhukovsky | Shutterstock

In the US, however, a maximum of four digits are used for flights. American Airlines, the national airline of the US, operates 6700 flights a day. Given that there are 9999 digits to choose from, you might think that the problem is not too concerning. However, there was a report that said that at a recent American Airlines meeting, the possibility of running out of flight numbers was discussed. An IT employee (at the airline) considered whether using a five-digit number was the right way to go.

The restrictions on the flight numbers used have been extended

In 2019, The Points Guy reported that AA actually had a limit of 2,949 flight numbers they could use for mainline flights:

“At American, flights 1 through 2949 are all assigned to the main fleet, while flights 2950 through 6099 are reserved for numerous regional partners such as Skywest or Envoy. Delta and United use a similar formula. This allows route planners and other employees to quickly identify which airline is operating a flight and often where it is going.”

Photo: Markus Mainka | Shutterstock

However, in April of this year, this changed when American Airlines increased the number of flights it used. The number of mainline flights was increased to 3,139. ​​Some examples of this were:

• AA30006 was used on American Airlines flights from Raleigh–Durham International Airport (RDU) to Phoenix Sky Harbor International Airport (PHX) with their Boeing 737 aircraft.
• AA30009 was used on American Airlines flights from Eagle County Regional Airport (EGE) to Dallas-Fort Worth International Airport (DFW) with their Airbus A319 aircraft.
• AA3001 was used on American’s Airbus A321 flights from Los Angeles International Airport to Louisville Muhammad Ali International Airport (SDG).

But extending the numbers to flights is not so easy

One might wonder why the issue of missing flight numbers is such a big problem. After all, we could extend a three-digit flight number system to four, a four-digit one to five, and so on. However, the solution is not as simple as it seems. Viewfromthewing.com reported that the solution would require updating the systems that airlines have been using for more than half a decade:

“The computer systems that airlines use are based on systems that are sixty years old, so it’s difficult to adapt to that. And as with Y2K*, older systems have skimped on data size for storage and processing reasons.”

Use of abbreviations and other solutions

The problem of no longer adhering to the four-digit limit on flight numbers doesn’t really exist (at least for now), except for American Airlines, Delta Air Lines and United Airlines. Just as the phrase “Year 2000” could be parsimoniously written as Y2K, United used the abbreviation system for its elite status nomenclature, viewfromthewing.com reported:

“Abbreviations were used. That’s how United Airlines’ elite status levels got their names, for example. ‘1K’ was used instead of 1000K or 100,000 miles because there were only two digits to denote them. It was intended as an internal designation, not for the public, but it eventually stuck.”

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Perhaps such a solution is in sight. Another solution could be to assign the same flight number to multiple daily flights. However, this could lead to problems like those that occurred in India a few years ago. After multiple flights were assigned the same numbers, the Joint Director General and Head of Security of DGCA had to address the issue publicly:

“Even after careful consideration of call sign conflicts last season, airlines are announcing new flights with similar call signs within 15 minutes on the same route. They have been advised to take note of the guidelines on the call sign conflict issue.”

Photo: China Southern

As aviation becomes more accessible to more people, extending three-digit flight numbers to four-digit ones or four-digit flight numbers to five-digit ones may be the only sensible solution. The same goes for introducing alphabetic letters. However, the aviation community is watching closely to see when this technological shift will take place.